This species is distinguished from congeners by the following combination of characters: Small shore flies, body length 1.60–1.90 mm. Head: Subglobose, very broad ventrally, oral opening comparatively large. Antennal coloration variable, entirely yellow to nearly evenly divided between yellowish and dark gray, dorsal and anterior surfaces of pedicel and basal flagellomere extensively dark gray. Parafacial silvery white, concolorous with face; gena-to-eye ratio 0.20–0.23. Thorax: mesonotum yellowish to golden brown; pleural area gray. Wing with costal vein ratio 0.72–0.81; M vein ratio 0.43–0.44. Forefemur bearing a distinctive, comb-like row of stout setulae along anteroventral and posteroventral surfaces; tibiae mostly gray; hindtibia bearing a large, spur-like seta ventroapically. Abdomen: Tergites 1–4 with dorsum mostly grayish brown, with lateral margin unevenly demarcated from silvery gray to gray portion, lacking grayish wedges laterally on tergites 2–4; tergite 5 light gray to silvery gray, similar to coloration along lateral margins of preceding tergites but with posterior margin blackish brown to slate black, similar to coloration of medial area on tergites 1–4; medial coloration on tergites 1–4 wide, occupying most of dorsum, dark, grayish to slate black. Male terminalia (Figs 2–5): Combined structures generally moderately elongate, in posterior view (Fig. 2) height less than twice width, generally setulose; epandrium with dorsal arch above cerci narrowly developed, completely connected, in posterior view (Fig. 2) as an inverted, rounded U on dorsal half, ventral half more narrowly developed than dorsal portion, lateral margins shallowly curved medially, deeply bifurcate medially, medial bifurcation as wide as ventral epandrial arm, narrowly pointed apically, bearing longer setulae along dorsal arch and at midheight, in lateral view (Fig. 3) narrowly rectangular on dorsal 1/4, nearly vertical, thereafter ventrally oriented anteroventrally, more thickly developed, apical 1/3 tapered to narrowly rounded apex; cerci moderately long, height about 2.5× width, semi-hemispherical (Fig. 2), not attached lateroventrally with epandrium; aedeagus in lateral view (Fig. 5) elongate, parallel sided, about 8× longer than width, tubular, shallowly sinuous, with apical portion moderately pointed, in ventral view (Fig. 4) mostly parallel sided on basal 2/3 except for immediate base that is tapered medially, apical 1/3 abruptly narrowed, slightly spatulate, apex narrow, rounded; phallapodeme in lateral view (Fig. 5) somewhat narrow, moderately elongate, unevenly bar-like with medial margin shallowly arched, keel skewed toward attachment with hypandrium, narrow but extended, extended margin roundly rectangular, in ventral view (Fig. 4) broadly as a short T with arms short and triangular; gonite in lateral view (Fig. 5) narrow, elongate, bar-like, shallowly sinuous, in ventral view (Fig. 4) very shallowly curved; hypandrium in lateral view (Fig. 5) elongate, shallow, tapered at both apices, more narrowly so posteriorly, in ventral view (Fig. 4) with posterior half to 2/3 spindle shaped, becoming wider with short extended lateral processes just before posterior margin, posterior margin shallowly emarginated, anterior portion as an arrowhead with posteriorly directed robust extensions and with lateral and anterior margins shallowly arched, roundly pointed.

The holotype male of Hydrochasma castilloi is labeled “Ecuador[.]Loja Catamayo Dec. 1955/Collr.Levi-Castillo/USNM ENT 00118297 [plastic bar code label]/HOLOTYPE ♂ Hydrochasma castilloi Mathis & Zatwarnicki, USNM [red].” The holotype is double mounted (glued to a paper triangle)), is in excellent condition, and is deposited in the USNM. Sixteen paratypes (11♂, 9♀; USNM) bear the same label data as the holotype.

Ecuador. Loja: Catamayo (03°59'S, 79°21'W), Dec 1955.

ECUADOR. El Oro: Puerto Bolivar (03°16'S, 79°60'W), Dec 1955, R. Levi-Castillo (1♂, 2♀; USNM). Guayas: Cone (02°10.1'S, 79°38'W), Jun 1955, R. Levi-Castillo (1♀; USNM).

(Fig. 6). Neotropical: Ecuador (El Oro, Guayas, Loja).

The specific epithet, castilloi, is a genitive patronym to honor Roberto Levi-Castillo, the collector of the type series and many other shore flies from Ecuador.

This species has been frequently misidentified as Hydrochasma patens in collections. Our study of the holotype of Hydrochasma patens, however, reveals it to be a separate and distinct, although closely related species. Fortunately, the structures of the male terminalia are very diagnostic and distinctive. These structures in Hydrochasma castilloi are generally much more robust and shorter in both posterior and lateral views (Figs 2–5). In addition, the aedeagus in lateral view (Fig. 5) is shallowly sinuous, and the hypandrium in ventral view (Fig. 4) has much shorter, posterolateral processes. In Hydrochasma patens, the aedeagus in lateral view is shallowly arched, not sinuous, and the posterolateral hypandrial processes are three to four times longer than those of Hydrochasma castilloi. In general form, structures of the male terminalia of this species are more similar to those of Hydrochasma faciale and Hydrochasma williamsae, being relatively short and robustly developed. The dorsum of the epandrium in Hydrochasma castilloi is complete though thinly developed; whereas in Hydrochasma faciale and Hydrochasma williamsae, the dorsal band is incomplete resulting in an open dorsal margin to the cercal cavity.

This species is distinguished from congeners by the following combination of characters: Small shore flies, body length 1.25–1.90 mm. Head: Subglobose generally, very broad ventrally, oral opening comparatively large. Antenna mostly dark gray; at least pedicel black. Parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.21–0.24. Thorax: Mesonotum yellowish to golden brown; pleural area gray. Wing with costal vein ratio 0.93–0.96; M vein ratio 0.44–0.46. Forefemur bearing a distinctive, comb-like row of stout setulae along anteroventral surface; tibiae mostly gray; hindtibia bearing a long, spur-like seta ventroapically. Abdomen: Tergites broadly darker gray medially, becoming lighter gray laterally but unevenly, lacking wedge-shaped gray to silvery gray areas or a sharply contrasted demarcation between dorsal and lateral coloration; tergite 5 of male gray. Male terminalia (Figs 7–10): Combined structures generally moderately elongate, in posterior view height not quite twice width; epandrium with dorsal arch interrupted medially, not connected above cerci; generally sparsely setulose; in posterior view (Fig. 7) as an inverted, divergent U on dorsal third, medial portion with lateral margins angled medially, robustly developed, ventral apical portion somewhat rectangular, lateral margins (height less than that of cerci) parallel sided, partially bifurcate, narrowly and deeply incised medially, broadly truncate apically, in lateral view (Fig. 8) widely notched and with a robust, curved, partially hook-like ventral process; cerci moderately long, height about 1.5× width (Fig. 7), tenuously attached ventrolaterally with epandrium; aedeagus in lateral view (Fig. 10) moderately elongate, about 2.5× longer than greatest width, tubular, slightly wider basally and more so apically, with apical portion unevenly rounded, in ventral view (Fig. 9) moderately wide basally, thereafter tapered medially but just before apex, apex distinctly but narrowly extended laterally; phallapodeme in lateral view (Fig. 10) broad and short with width subequal to length, keel wide and long, extended margin irregularly rounded, in ventral view (Fig. 9) narrowly T-shaped with arms short and right angled; gonite in lateral view (Fig. 10) narrow, moderately elongate, bar-like, slightly arched, in ventral view (Fig. 9) more conspicuously curved; hypandrium in lateral view (Fig. 10) elongate, shallow, anterior 1/3 obtusely angled, parallel sided, in ventral view (Fig. 9) with posterior third divergently U-shaped, anterior portion slightly narrower, plate-like, anterior margin broadly rounded.

The holotype male of Hydrochasma crenulum is labeled “PERU. Cuzco: Pau-cartambo, Atalaya, R[ío]. AltoMadredeDios, 600m, 4Sep1988, WNMathis/USNM ENT 00092795 [plastic bar code label]/HOLOTYPE ♂ Hydrochasma crenulum Mathis & Zatwarnicki, USNM [red].” The holotype is double mounted (minuten in a block of plastic), is in excellent condition, and is deposited in the USNM. Fifty paratypes (34♂, 16♀; USNM) bear the same label data as the holotype.

Peru. Cuzco: Paucartambo, Atalaya (Río Alto Madre de Dios; 12°53.3'S, 71°21.6'W; 600 m).

Neotropical. PERU. Madre de Dios: Diamante (Río Alto Madre de Dios; 12°19.9'S, 70°57.5'W; 400 m), 7 Sep 1988, W. N. Mathis (4♂, 10♀; USNM); Río Manu, Erika (near Salvación; 12°50.7'S, 71°23.3'W; 550 m), 5-6 Sep 1988, W. N. Mathis (4♂, 2♀; USNM).

(Fig. 6). Neotropical: Peru (Cuzco, Madre de Dios).

The species epithet, crenulum, is of Latin derivation and means notched, referring to the conspicuous notch in the epandrium that is best seen in lateral view.

The shapes of structures of the male terminalia of Hydrochasma crenulum are unmistakable and readily distinguish this species from congeners, especially those of the faciale group. This is especially evident in the ventral portion of the epandrium in lateral view that is generally robustly developed, is conspicuously and widely notched, and terminates as an extended, curved process.

This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.40–1.90 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.15–0.17. Thorax: Wing with costal vein ratio 0.77–0.81; M vein ratio 0.47–0.49. Forecoxa whitish gray to gray; hindtibia with prominent ventroapical, shallowly curved, spur-like seta. Abdomen: Tergites broadly brown medially, becoming lighter gray laterally but unevenly, almost shallowly wedge-like, tergite 5 of male gray with a thin, medial brown stripe (Fig. 12). Male terminalia (Figs 13–16): Combined structures generally moderately elongate, in posterior view height over 2× width, generally setulose on cerci, setulae sparse or minute ventrally; epandrium with dorsal arch above cerci not interrupted, narrowly connected, in posterior view (Fig. 13) with basal 1/2 somewhat rectangular with angles rounded, apical 1/2 narrowed, extended as separate, narrow, almost parallel sided processes with a deep and moderately wide gap between processes, lateral margins very shallowly arched, each process rounded apically, in lateral view (Fig. 14) generally shallowly arched with curvature relatively even, widest just ventrad of cercus, apical third abruptly narrowed, tapered, curved anteriorly subapically, apex narrowly rounded, bearing minute setulae; aedeagus in lateral view (Fig. 16) elongate, narrow, irregularly tubular, shallowly curved, gradually tapered on basal 3/4, thereafter widened to form a boxlike apex (angles rounded), in ventral view (Fig. 15) mostly parallel sided on basal 2/3, apical 1/3 more narrowed but still parallel sided, apex rounded; phallapodeme in lateral view (Fig. 16) oriented perpendicular to aedeagus, narrowly elongate, keel very evident as an extension on portion toward hypandrium, portion toward aedeagal base rod-like in ventral view (Fig. 15) as a short, rounded, isosceles triangle with a circular structure at base, foreshortened; gonite in lateral view (Fig. 16) rod-like, straight, narrow, in ventral view (Fig. 15) short due to foreshortening; hypandrium in lateral view (Fig. 16) elongate, comparatively wide, anterior margin narrowly rounded, posterior margin as 2 narrow, elongate processes, which form a deep gap between, posterior projection acutely pointed and shorter than anterior projection, in ventral view (Fig. 15) as an arrowhead that is deeply incised posterolaterally with a tapered, elongate, acutely pointed, posterolateral projection, base extended posteriorly, parallel sided along middle portion, thereafter flared posterolaterally as 2 symmetrical processes, forming a wide, V-shaped posterior margin.

The holotype male of Hydrochasma digitatum is labeled “PERU. Madre de Dios: Manu, Diamante, 400 m, 12°25' [sic 19.9']S, 70°57[.5]'W, R[ío]. AltoMadre de Dios, 7 Sep 1988, W.N.Mathis/USNM ENT 00285974 [plastic bar code label]/HOLOTYPE ♂ Hydrochasma digitatum Mathis & Zatwarnicki, USNM [red].” The holotype is double mounted (minuten in a block of plastic), is in excellent condition, and is deposited in the USNM. Thirteen paratypes (3♂, 10♀; USNM) bear the same label data as the holotype.

Peru. Madre de Dios: Diamante (Río Alto Madre de Dios; 12°19.9'S, 70°57.5'W; 400 m).

Neotropical. PERU. Cuzco: Paucartambo, Atalaya (Río Alto Madre de Dios; 12°53.3'S, 71°21.6'W; 600 m), 4 Sep 1988, W. N. Mathis (1♂; USNM). Madre de Dios: Río Manu, Erika (near Salvación; 12°50.7'S, 71°23.3'W; 550 m), 5–6 Sep 1988, A. Freidberg, W. N. Mathis (2♂, 1♀; USNM).

(Fig. 17). Neotropical: Peru (Cuzco, Madre de Dios).

The species epithet, digitatum, is of Latin derivation and refers to the finger-like ventral extensions of the epandrium.

This species, as implied by its name, is distinguished from congeners by the elongated, slender, very shallowly curved, digitiform, ventral epandrial processes. These digitiform processes are separated from each other in posterior view by a deep, narrowly U-shaped pocket or gap. In lateral view, these processes are tapered and slightly curved subapically.

This species is distinguished from congeners by the following combination of characters: Small to moderately small shore flies, body length 1.40–2.50 mm. Head: Head subglobose, very broad ventrally, oral opening comparatively large; antennal coloration variable, entirely yellow to nearly evenly divided between yellowish and dark gray, dorsal and anterior surfaces of pedicel and basal flagellomere extensively dark gray; parafacial silvery white, concolorous with face (Figs 18–20); gena-to-eye ratio 0.25–0.28. Thorax: Mesonotum yellowish to golden brown; pleural area gray. Wing with costal vein ratio 0.71–0.75; M vein ratio 0.54–0.56. Forefemur bearing a distinctive, comb-like row of stout setulae along anteroventral surface; tibiae mostly gray; hindtibia bearing a large, spur-like seta ventroapically. Abdomen: Tergites broadly brown medially, lacking wedge-shaped, gray to silvery gray areas laterally; tergite 5 of male brown, concolorous with tergites 2–4. Male terminalia (Figs 21–24): Combined structures generally slightly elongate, in posterior view height about 1.5× width, generally setulose, especially dorsally but also along ventral margins; epandrium with dorsal arch above cerci attenuated, not connected, in posterior view (Fig. 21) with cercal cavity forming a U, with arms of U robustly developed, ventral portion with each lateral half robustly developed, tapered to ventral apex, apex pointed, deeply and narrowly incised medially, medial incision 3× longer than wide, widest at apex, in lateral view (Fig. 22) with ventral portion robust, apex obtusely pointed; cerci moderately long, height more than twice width, widely semi-hemispherical (Fig. 21), pointed dorsally, not attached lateroventrally or ventrally with epandrium; aedeagus in lateral view (Fig. 24) elongate, almost 4× longer than width, tubular, shallowly curved, apex rounded, in ventral view (Fig. 23) mostly tapered from base to pointed apex, apical third more abruptly tapered; phallapodeme in lateral view (Fig. 24) triangular with extended keel skewed and pointed on portion toward attachment with hypandrium, in ventral view (Fig. 23) an elongate, moderately robust T with double crosses, arms of cross short; gonite in lateral view (Fig. 24) narrow, moderately elongate, bar-like, very shallowly curved, in ventral view (Fig. 23) shallowly curved; hypandrium in lateral view (Fig. 24) moderately elongate, sack-like, moderately wide, tapered to point posteriorly, anterior margin broadly rounded, in ventral view (Fig. 23) very broadly and robustly U-shaped, with tiny, pointed lateral extensions from base laterally.

The lectotype male of Discocerina faciale Williston (designated by Mathis and Edmiston 1991: 825) is labeled “Co-type [circular label with a yellow border]/Windward side St. Vincent, W.I. H. H. Smith./W.Indies. 1907-66./Discocerina facialis Will. [handwritten, two red submarginal borders]/LECTOTYPE Discocerina facialis Will. ♂ By W. N.Mathis [handwritten except for “LECTOTYPE” and “By”, black sub-border].” The lectotype is double mounted (pin in rectangular piece of cardboard), is in poor condition (right foreleg, mid legs missing), and is deposited in the BMNH. There is also one female paralectotype (BMNH). Williston, in the original description, noted “Five specimens. St. Vincent.” The other syntypes (1♂, 2♀; BMNH) are apparently representatives of Hydrochasma incisum (no silvery triangular patches on dorsum of abdomen).

The lectotype male of Hydrochasma zernyi Hendel, here designated to preserve stability and make more universal the use of this name, is labeled “Unt. Amazonas [Brazil. Pará] Santarem 18. VIII 27. [18 Aug 1927] Zerny [“18. VIII” handwritten]/Hydrochas-ma Zernyi H. [handwritten]/Type [red]/LECTOTYPE ♂ Hydrochasma zernyi Hendel By Mathis & Zatwarnicki [handwritten except for “LECTOTYPE” and “By”; black sub-border].” The lectotype is double mounted (minuten in a rectangular block of foam plastic), is in good condition, and is deposited in NMW. There are also four (3♂, 1♀) paralectotypes in the NMW that bear the same locality label.

The holotype female of Hydrochasma capax Cresson is labeled “Gualan Guatemala 2–15 [handwritten] [19]05/1096/TYPE Hecamedoides CAPAX E.T. Cresson, Jr. [species name handwritten].” The holotype is double mounted (paper triangle), is in good condition (mid- and hindlegs on right side missing), and is deposited in the ANSP (6533).

West Indies. St. Vincent (13°10'N, 61°14'W).

Nearctic. UNITED STATES. ARIZONA. Pima: near Kits Peak, Baboquivari Mountains (32°00N, 111°36'W), 7-8 Aug 1916 (1♀; ANSP).

CALIFORNIA. San Diego: San Diego (32°42.9'N, 117°09.4'W; lakeside), 4 Aug 1931, J. M. Aldrich (1♂; ANSP).

Neotropical. BELIZE. Stann Creek: Dangriga (16°58'N, 88°13'W), 3-4 Apr 1993, W. N. Mathis (3♂, 2♀; USNM); Twin Cays (south end of East Island; 16°49.4'N, 88°06.3'W), Mar 1988, W. N. Mathis (1♂; USNM).

BRAZIL. Paraná: Morretes (25°28'S, 48°59.1'W), 29 Aug 2000, W. N. and D. Mathis (9♂, 3♀; USNM). São Paulo: Ubatuba, Praia Puruba (23°21'S, 44°55.6'W; beach), 29 Mar 2010, D. and W. N. Mathis (9♂, 1♀; DZUP, USNM).

GUYANA. Karanambo, Rupununi River (ox bow; 03°45.1'N, 59°18.6'W), 2 Apr 1994, W. N. Mathis (1♂, 1♀; USNM); Kato, Chiung River (04°39.7'N, 59°50.0'W), 1 May 1995, W. N. Mathis (2♂; USNM); Moco-Moco (30 km E Lethem in Kanuku Mountains; 03°18.2'N, 59°39.0'W), 29 Apr 1995, W. N. Mathis (2♂; USNM); Pirara Ranch and River (03°32.1'N, 59°40.5'W), 24–25 Apr 1995, W. N. Mathis (9♂, 13♀; USNM).

TRINIDAD and TOBAGO. Tobago. St. John: Speyside (11°18'N, 60°32'W), 13-15 Jun 1993, W. N. Mathis (2♂, 2♀; USNM).

West Indies. CUBA. Pinar del Rio: Soroa (22°47.7'N, 83°W), 4-6 Dec 1994, W. N. Mathis (6♂, 12♀; USNM); Soroa (2 km E; 22°47.7'N, 83°W), 29 Apr 1983, W. N. Mathis (1♀; USNM).

DOMINICA. Cabrits Swamp (15°35'N, 61°29'W), 22-25 Mar 1965, W. W. Wirth (1♀; USNM); Layou River mouth (15°23.6'N, 61°25.5'W), 9 Jan-24 Mar 1965, W. W. Wirth (43♂, 44♀; USNM); Macoucheri (15°26.6'N, 61°27'W; seashore), 1 Feb-8 Mar 1965, W. W. Wirth (2♂, 2♀; USNM); Rosalie (15°22.3'N, 61°15.3'W), 23 Mar 1989, W. N. Mathis (2♂, 2♀; USNM).

DOMINICAN REPUBLIC. La Vega: Constanza (ca. 16 km SE; 18°50.6'N, 70°40.7'W; 1580 m), 15 May 1998, D. and W. N. Mathis (1♂; USNM); El Rio (9.5 km E; 19°0.9'N, 70°33.5'W; 980 m), 6-7 May 1995, W. N. Mathis (1♂, 1♀; USNM); Jarabacoa (1-2 km S; 19°06.9'N, 70°37'W; 520 m), 8-21 May 1995, W. N. Mathis (1♂; USNM); Rio Camu (3.5 km NW La Vega; 19°13.7'N, 70°35.2'W; 100 m), 10 May 1995, W. N. Mathis (9♂, 4♀; USNM); Salto Baiguate (near Jarabacoa; 19°05.5'N, 70°36.9'W; 570 m), 9 May 1995, W. N. Mathis (1♂; USNM). Peravia: San José Ocoa (10 km NE; 18°35'N, 70°25.6'W), 21 May 1998, D. and W. N. Mathis (1♀; USNM). Puerto Plata: Rio Camu (14 km E Puerto Plata; 19°41.9'N, 70°37.4'W), 17 May 1995, 1997, D. and W. N. Mathis (6♂, 3♀; USNM); Rio Pérez (near Imbert; 19°44.1'N, 70°50.2'W), 24 May 1998, D. and W. N. Mathis (6♂, 1♀; USNM).

GRENADA. St. George: Beauséjour Bay (12°05.5'N, 61°44.9'W), 21 Sep 1996, W. N. Mathis (1♂; USNM). St. John: Palmiste (12°08.7'N, 61°44.4'W), 21 Sep 1996, W. N. Mathis (3♂, 1♀; USNM). St. Patrick: Levera Bay (12°13.6'N, 61°36.6'W), 18 Sep 1996, W. N. Mathis (2♂; USNM).

JAMAICA. Clarendon: Grantham (18°09.3'N, 77°23.8'W; 340 m), 16 Apr 2000, W. N. Mathis (5♂; USNM). Portland: Berridale (18°06.5'N, 76°20'W), Rio Grande River, 25 Apr 2000, W. N. Mathis (6♂; USNM). St. Andrew: Mavis Bank (1.7 km E; 18°02.4'N, 77°39.5'W; 575 m), Yallahs River, 21-22 Apr-1 May 2000, W. N. Mathis (3♂, 4♀; USNM); Mavis Bank (4.3 km SE; 18°01.4'N, 76°38.1'W; 480 m); Yallahs River, 22-23 Apr 2000, W. N. Mathis (1♂; USNM). St. Thomas: Bath Fountain Spring (17°57.6'N, 76°21.3'W), 15 May 1996, D. and W. N. Mathis, H. B. Williams (3♀; USNM); Bath River, Bath (17°56.8'N, 76°21.6'W), 16 May 1996, D. and W. N. Mathis, H. B. Williams (8♂, 2♀; USNM); Hagley Gap (1 km E; 18°00.1'N, 76°36.7'W), 16 May 1996, D. and W. N. Mathis, H. B. Williams (1♂, 1♀; USNM); Mt. Lebanus (17°58.2'N, 76°32.7'W), 16 May 1996, D. and W. N. Mathis, H. B. Williams (2♂; USNM); Yallahs River (mouth; 17°53'N, 76°35.6'W), 14 May 1996, D. and W. N. Mathis, H. B. Williams (1♂, 2♀; USNM).

PUERTO RICO. Adjuntas (18°09.8'N, 66°43.2'W), 22 Sep 1995, D. and W. N. Mathis (10♂, 5♀; USNM).

ST. LUCIA. Dauphin Boguis (1.6 km S Marquis; 14°01'N, 60°55'W), 17 Jun 1991, D. and W. N. Mathis (3♂, 5♀; USNM); Micoud (13°49'N, 60°54'W), 15 Jun 1991, D. and W. N. Mathis (1♂; USNM); Soufrière (beach; 13°51'N, 60°54'W), 11-12 Jun 1991, D. and W. N. Mathis (3♂, 1♀; USNM).

ST. VINCENT. Charlotte: Colonarie (13°14.4'N, 61°06.9'W; beach), 29 Mar 1989, W. N. Mathis (2♂; USNM); Spring (13°11.1'N, 61°08.5'W), 6 Sep 1997, W. N. Mathis (2♂, 2♀; USNM). St. Andrew: Buccament Bay (near beach; 13°11'N, 61°16'W), 25-28 Mar-8 Jun 1989, 1991, D. and W. N. Mathis (20♂, 23♀; USNM); Layou (13°12'N, 61°17'W), 8 Jun 1991, D. and W. N. Mathis (2♂, 1♀; USNM). St. David: Richmond Beach (13°18.6'N, 61°14.1'W), 28 Mar 1989, W. N. Mathis (1♀; USNM). St. Patrick: Cumberland Bay (13°16'N, 61°16'W), 28 Mar-8-15 Sep 1989, 1991, 1997, A. Freidberg, D. and W. N. Mathis (20♂, 10♀; USNM); Cumberland River (3 km E Spring Village; 13°15'N, 61°14'W), 10 Jun 1991, D. and W. N. Mathis (19♂, 2♀; USNM); Wallilabou (beach; 13°15'N, 61°16'W), 27 Mar 1989, W. N. Mathis (5♂, 10♀; USNM).

(Fig. 25). Nearctic: United States (Arizona, California). Neotropical: Belize (Stann Creek), Brazil (Pará, Paraná, São Paulo), Guatemala, Guyana, Trinidad and Tobago, West Indies (Cuba, Dominica, Dominican Republic, Grenada, Jamaica, Puerto Rico, St. Lucia, St. Vincent).

Natural History.-This species occurs along freshwater streams and rivers or sometimes brackish water systems (where a freshwater stream or river is entering the ocean) that have sandy areas that are mostly bare of vegetation.

We follow Wirth (1968) in recognizing the two junior synonyms of Hydrochasma faciale, as noted in the synonymy.

Although this species is externally similar to Hydrochasma williamsae, as are structures of the male terminalia, they are distinguished from each other in details of the latter structures. The epandrium of this species, for example, is broadly rounded dorsolaterally, not angulate as in Hydrochasma williamsae, and the ventral margin in lateral view is robustly developed and broadly but unevenly rounded apically, not tapered and pointed as in Hydrochasma williamsae.

This species is distinguished from congeners by the following combination of characters: Small to moderately small shore flies, body length 1.85–2.60 mm. Head: Subglobose, very broad ventrally, oral opening comparatively large. Pedicel mostly black; medial surface of basal flagellomere extensively yellow, lateral surface with some blackish coloration. Parafacial silvery white, concolorous with face; gena-to-eye ratio 0.32–0.35. Thorax: Mesonotum generally gray but with faint bluish or slightly greenish metallic coloration, especially on posterior portion, including scutellum, not on notopleuron or lateral margins of scutellum; pleural area gray. Wing with costal vein ratio 0.50–0.62; M vein ratio 0.49–0.51. Femora and tibiae gray, tarsi yellow; forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface but with a posteroventral row of 5–7 short, spine-like setae; hindtibia bearing a long, spur-like seta ventroapically. Abdomen: Tergites generally dull gray, becoming brownish gray medially; lacking wedge-shaped, gray to silvery gray areas; tergite 5 gray. Male terminalia (Figs 26–29): Combined structures generally moderately elongate, in posterior view height slightly less than 3× width, generally sparsely setulose, especially dorsally; epandrium with dorsal arch above cerci relatively well developed, thin, completely connected, in posterior view (Fig. 26) as an inverted U on dorsal third to half, ventral portion with lateral margins shallowly concave medially, cruciate subapically, deeply bifurcate medially, medial bifurcation almost as wide as ventral process of epandrium at same level, extended epandrial process tapered, apex rounded; cerci moderately long, height nearly twice width, widely semi-hemispherical (Fig. 26), not attached lateroventrally with epandrium; aedeagus in lateral view (Fig. 29) elongate, about 5× longer than wide, tubular, shallowly curved, slightly tapered toward apex with apical portion moderately pointed and with a subapical, rounded projection, in ventral view (Fig. 28) mostly tapered from base to pointed apex; phallapodeme in lateral view (Fig. 29) narrowly triangular with extended keel skewed and pointed on portion toward attachment with hypandrium, in ventral view (Fig. 28) an elongate, robust T with crossbar very short; gonite in lateral view (Fig. 29) narrow, elongate, bar-like, very shallowly curved and spatulate, in ventral view (Fig. 28) shallowly curved; hypandrium in lateral view (Fig. 29) elongate, moderately shallow, tapered at both apices and with lateral, posteriorly directed process evident, in ventral view (Fig. 28) with posterior half spindle shaped, becoming wider with long extended lateral processes just before posterior margin, posterior margin deeply emarginated, emargination V-shaped, anterior portion as an arrowhead with posteriorly directed narrow, elongate, lateral extensions and with lateral and anterior margins shallowly arched, forming a V-shaped anterior margin.

The holotype male of Hydrochasma patens is labeled “Holo- type [round label with red margin]/9100/Uruguay: Montevideo, 21–22. i. 1927 [21–22 Jan 1927]. F. & M. Edwards. B. M. 1927–63/TYPE Hydrochasma PATENS E. T. Cresson, Jr. [carmine; Hydrochasma PATENS handwritten]”. The holotype is double mounted (minuten in a plastic rectangle), is generally in good condition (lacking left foretarsus), and is deposited in the BMNH.

Uruguay. Montevideo: Montevideo (34°53.3'S, 56°11'W).

Neotropical. CHILE. Osorno: Lago Puyehue (SE shore; 40°45'S, 72°25.2'W), 10 Feb 1978, W. N. Mathis (3♂, 10♀; USNM). Talca: Rio Lircay (11 km N Talca; 35°23'S, 71°39'W; 85 m), 23 Jan1978, W. N. Mathis (22♂, 31♀; USNM).

(Fig. 30). Neotropical: Uruguay, Chile (Osorno, Talca).

The identity of this species has been confused, resulting in misidentifications in collections that we have examined. Structures of the male terminalia of this species are distinctive, however, and distinguish it from congeners, especially the elongated and slender general conformation of these structures, which can only be mistaken with those of Hydrochasma viridum. Both of these species have elongated, very slender, ventrolateral epandrial processes that are very similar. The hypandrium, especially in ventral view, however, has more elongated, posterolaterally directed processes in Hydrochasma patens. Additionally, the dorsum of the head and the mesonotum are mostly gray with only faint bluish or greenish coloration.

This species is distinguished from other congeners by the following combination of characters: Small to moderately small shore flies, body length 1.55–2.00 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.27–0.30. Thorax: Wing with costal vein ratio 0.62–0.65; M vein ratio 0.57–0.60. Forefemur with comb-like row of distinct, short, stout setulae along apical half of posteroventral margin; hindtibia bearing a short seta, length subequal to width at same level. Abdomen: Tergites broadly dark gray medially, lacking wedge-shaped, gray to silvery gray areas laterally; tergite 5 of male mostly gray but with vague, slate gray medial stripe. Male terminalia (Figs 31–34): Combined structures generally moderately elongate, in posterior view height less than twice width (1.85×), generally setulose on cerci, setulae sparse or minute ventrally; epandrium with dorsal arch above cerci not interrupted, narrowly connected, in posterior view (Fig. 31) with basal 1/2 somewhat ovate, apical 1/2 moderately narrowed, extended as 2 separate, moderately narrow, almost parallel sided processes with a deep, narrow gap between processes, lateral margins sinuous, each process narrowly rounded apically, in lateral view (Fig. 32) generally narrowly triangular on ventral 2/3, tapered, straight, widest just ventrad of cercus, apical third tapered, straight, apex narrowly rounded, bearing minute setulae; aedeagus in lateral view (Fig. 34) simple, straight, tubular, in ventral view (Fig. 33) mostly parallel sided on basal 2/3–3/4, apical 1/4 tapered to bluntly rounded apex; phallapodeme in lateral view (Fig. 34) oriented perpendicular to aedeagus, robustly elongate, keel evident as an extension on portion toward hypandrium, portion toward aedeagal base tapered, in ventral view (Fig. 33) pedunculate with double T with arms short and thin, perpendicular; gonite apparently lacking; hypandrium in lateral view (Fig. 34) elongate, comparatively narrow, deeply hook-like, anterior margin narrowly rounded, extension narrow, parallel sided, elongate, in ventral view (Fig. 33) more or less rectangular, with deeply incised posterolateral, short, narrow projections, posterior extensions robust, slightly flared posterolaterally, with deep pocket between, forming a U-shaped posterior margin.

The holotype male of Hydrochasma rictum is labeled “HONDURAS. Cortés:San Pedro Sula (8 km S) 15°25.7'N, 88°01.4'W[, ] 25–26 September1995[, ] Dianne & W.N.Mathis/USNM ENT 00138958 [plastic bar code label]/HOLOTYPE ♂ Hydrochasma rictum Mathis & Zatwarnicki, USNM [red].” The holotype is double mounted (minuten in a block of plastic), is in good condition (abdomen and hindlegs removed, abdomen dissected, parts in an attached microvial), and is deposited in the USNM. A female paratype bears the same label data as the holotype.

Honduras. Cortés: San Pedro Sula (8 km S; 15°25.7'N, 88°01.4'W).

Neotropical. COSTA RICA. Guanacaste: Playa Puerto Soley (11°02.5'N, 85°40.1'W; beach), 16 Jun 2003, D. and W. N. Mathis (1♂, 1♀; USNM). Limón: R. V. S. Gandoca-Manzanillo, desembocadura de Laguna Gandoca (09°35.4'N, 82°35.8'W), 18 May 2004, D. Briceño (1♂; INBIO).

(Fig. 35). Neotropical: Costa Rica (Guanacaste, Limon), Honduras (Cortés).

The species epithet, rictum, is of Latin derivation and means open mouth, referring to the large, open mouth of this species.

Structures of the male terminalia of this species are similar to those of Hydrochasma digitatum but are distinguished from that species in having more robustly developed ventral epandrial processes that are moderately angulate laterally in posterior view. Moreover, the hypandrium of this species in ventral view is much more robustly developed with a broad, bluntly rounded anterior margin.

This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.50–1.95 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena-to-eye ratio 0.18–0.20. Thorax: Wing with costal vein ratio 0.75–0.76; M vein ratio 0.47–0.49. Forecoxa whitish gray to gray. Hindtibia with prominent ventroapical, shallowly curved, spur-like seta. Abdomen: Tergites broadly slate gray medially, lacking wedge-shaped, gray to silvery gray areas laterally; tergite 5 of male gray with faint brown lateral margins, concolorous with tergites 2–4. Male terminalia (Figs 39–42): Combined structures generally moderately elongate, in posterior view height less than twice width (1.83×), dorsal half with setulae twice length of those on ventral half; epandrium with dorsal arch above cerci narrowly connected, in posterior view (Fig. 39) with dorsal margin arched, dorsal half as wide as high, apical half as 2 elongate, narrow, almost parallel sided processes, each oriented slightly medially, forming a deep, medial incision, in lateral view (Fig. 40) with anterior margin conspicuously sinuous, widest ventrad of cercus with a notch-like incision at base of ventral epandrial extension, ventral epandrial extension slightly tapered to rounded apex; cerci moderately elongate, height nearly twice width in posterior view, mostly semi-hemispherical (Fig. 39); aedeagus in lateral view (Fig. 42) elongate, narrow, nearly straight, length about 4× width, tubular, in ventral view (Fig. 41) shallowly emarginate at base, mostly parallel sided on basal half, apical half tapered to narrowly rounded apex; phallapodeme in lateral view (Fig. 42) narrowly elongate, keel very shallow and short, barely evident, in ventral view (Fig. 41) an elongate T with arms very short and thin, perpendicular; gonite in lateral view (Fig. 42) very narrowly elongate, bar-like, nearly straight, in ventral view (Fig. 41) as a robust, short comma; hypandrium in lateral view (Fig. 42) elongate, thin, very shallowly arched, in ventral view (Fig. 41) with elongate, narrow, lateral processes, each slightly more than half length of aedeagus, anterior margin shallowly incised, incision shallowly bifurcate.

The holotype male of Hydrochasma sinuatum is labeled “BELIZE. Stann Cr[ee]k. Dist[rict]. MullinsRiver[, ] (17km N Dangriga)[, ] 29 March 1988, Wayne N. Mathis/USNM ENT 00285977 [plastic bar code label]/HOLOTYPE ♂ Hydrochasma sinuatum Mathis & Zatwarnicki, USNM [red].” The holotype is double mounted (minuten in a block of plastic), is in excellent condition, and is deposited in the USNM. Fifteen paratypes (6♂, 9♀; USNM) bear the same label data as the holotype.

Belize. Stann Creek: Mullins Creek (17 km N Dangriga; 17°06.2'N, 88°17.8'W).

Neotropical. BELIZE. Stann Creek: Dangriga (16°58'N, 88°13'W), 3–4 Apr 1993, W. N. Mathis (18♂, 8♀; USNM); Silk Grass Creek (16°58'N, 88°13'W), 3 Apr 1993, W. N. Mathis (1♂, 1♀; USNM); Twin Cays, Aanderaa Flats (16°50'N, 88°06'W), 17–21 Mar 1988, W. N. Mathis (1♀; USNM); Twin Cays, West Bay (16°50'N, 88°06'W), 22 May 1988, W. N. Mathis (1♂; USNM).

COSTA RICA. Guanacaste: Santa Cruz (14 km S; 10°10.4'N, 85°35.7'W; 180 m), 23 Jun 2001, W. N. Mathis (1♂; USNM).

HONDURAS. Cortés: Omoa (16°47.8'N, 87°58.4'W), 26 Sep 1995, D. and W. N. Mathis (2♂, 2♀; USNM).

MEXICO. Sinaloa: Concordia (13 km NE; 23°20.7'N, 105°58.4'W), 15 Aug 1960, P. H. Arnaud, Jr., D. C. Rentz, E. D. Ross (7♂, 12♀; CAS, USNM).

PERU. Madre de Dios: Río Manu, Erika (near Salvación; 12°50.7'S, 71°23.3'W; 550 m), 5-6 Sep 1988, A. Freidberg, W. N. Mathis (2♂, 1♀; USNM).

(Fig. 43). Neotropical: Belize (Stann Creek), Costa Rica (Guanacaste), Honduras (Cortés), Mexico (Sinaloa), Peru (Madre de Dios).

The species epithet, sinuatum, is of Latin derivation and means winding or bent, referring to the shape of the extended epandrium in lateral view.

Although structures of the male terminalia of this species are similar to those of Hydrochasma digitatum, they consistently differ in detail. This is particularly evident in the shape of the ventral, epandrial processes where in lateral view there is a basal, posterior notch, and the processes themselves are sinuous and not shallowly arched, as in Hydrochasma digitatum. The sinuous profile of the ventral, epandrial process is the basis for the name of this species.

This species is distinguished from congeners by the following combination of characters: Small to moderately small shore flies, body length 1.50-2.30 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration; gena comparatively high, gena-to-eye ratio 0.47–0.50. Thorax: Wing with costal vein ratio 0.73–1.76; M vein ratio 0.42–0.46. Abdomen: Tergites lacking with broad, shallow, wedge-like marking laterally, otherwise tergites 2–4 with wide medial area extensively dark slate gray (Fig. 71); tergite 5 of male light gray to silvery gray anterior margin and thin, medial stripe brownish gray. Male terminalia (Figs 44–47): Combined structures moderately elongate, in posterior view height about twice width; epandrium with dorsal arch above cerci attenuate, not connected, dorsal 2/3 somewhat angulate laterally, gradually expanded to just ventrad of midheight, thereafter narrowed on ventral third, parallel sided, broadly rounded apically, rounded margin of apex with numerous, medially oriented, relatively robust setulae (Fig. 44), other epandrial setulae oriented medially, in lateral view very narrow dorsally (Fig. 45), lateral of cerci, thereafter ventrally nearly straight with slight, anterior angulate expansion at midheight, narrowly rounded apically; cerci short, in lateral view height about twice width (Fig. 45), narrowly semicircular, not attached with epandrium, narrowed ventrally; aedeagus in lateral view (Fig. 47) elongate, with length of sclerotized portion about 10× width, greatly enlarged ventroapically, membranous portion, shape irregular, in ventral view (Fig. 46) also showing expanded apex, spatulate, basal 2/3 narrowed, essentially parallel sided; phallapodeme in lateral view (Fig. 47) narrow, elongate, nearly straight, keel moderately weakly developed, evident at end toward attachment with hypandrium, in ventral view (Fig. 46) with hypandrial end T-shaped with crossbars forming concavity apically, thereafter toward base of aedeagus very gradually expanded to blunt apex; gonite in lateral view (Fig. 47) narrow, elongate, bar-like, obviously arched toward hypandrial end, in ventral view (Fig. 46) very narrow, shallowly arched; hypandrium in lateral view (Fig. 47) short, length about half that of phallapodeme, narrow, straight, bar-like, in ventral view (Fig. 46) widely U-shaped with very thin, pointed arms.

The holotype male of Hydrochasma spinosum is labeled “COSTA RICA. Limón: Westfalia (4 km S; 9°54.5'N, 82°59'W; beach), 27 Jun 2001, Amnon Freidberg/USNM ENT 00189486 [plastic bar code label]/HOLOTYPE ♂ Hydrochasma spinosum Mathis & Zatwarnicki, USNM [red].” The holotype is double mounted (minuten in a block of plastic), is in excellent condition, and is deposited in the USNM. Fifteen paratypes (10♂, 5♀; USNM) bear the same label data as the holotype or with W. N. Mathis as the collector.

Costa Rica. Limón: Westfalia (4 km S; 09°54.5'N, 82°59'W; beach).

Neotropical. COSTA RICA. Guanacaste: Bagaces Fortuna Z. P. Miravalles (10°43.1'N, 84°51.3'W; Sendero Cabro Muco; 980 m), 8–31 Jul 2002, J. D. Gutierrez (1♂, 2♀; INBio); Murciélago (10°56.5'N, 85°40.9'W), 1 Apr 1988, J. M. Hill, J. M. Mitchell, W. E. Steiner, J. M. Swearingen (2♂, 2♀; USNM); Nandayure, Estero Caletas (09°59.5'N, 85°15.2'W), 21 Mar-22 Oct 2003, D. Briceño (5♂, 1♀; INBio); Nandayure, Corozalito (10°0.1'N, 85°08.7'W), 23 Oct 2003, D. Briceño (2♀; INBio); Nandayure, Costa de Oro (09°55'N, 85°17'W; 11 m), 20 Oct 2003, D. Briceño (1♂, 1♀; INBio); Nandayure, Río Bejuco (09°50'N, 85°20'W; playa), 21 Oct 2003, D. Briceño (5♂, 1♀; INBio); Playa de Cuajiniquil (10°56.1'N, 85°42.2'W; beach), 16 Jun 2003, D. and W. N. Mathis (1♂; USNM). Limón: Guandoca, Manzanillo (09°36.8'N, 82°40.9'W), 19–25 May 2004, D. Briceño (1♂, 1♀; INBio); Talamanca, Cahuita (09°43.8'N, 82°50.7'W), 9–10 Dec 2001, E. Rojas (1♀; INBio). Puntarenas: Dominical (09°14.8'N, 83°51.4'W; 0–2 m), 11 Jun 2003, D. and W. N. Mathis (8♂, 1♀; USNM); Drake (08°41.4'N, 83°40.1'W; beach), 12 Aug 2001, D. and W.N. Mathis (1♀; USNM); Malpais (09°37.6'N, 85°09.1'W; beach), 21 Jun 2001, D. and W. N. Mathis (1♂, 2♀; USNM); Playa Jacó (09°36.5'N, 84°37.4'W; beach), 13 Jun 2003, D. and W. N. Mathis (5♂; USNM); Pochotal (09°31.4'N, 84°28.4'W; beach), 12–13 Jun 2003, D. and W. N. Mathis (8♂, 3♀; USNM); San Pedrillo (08°37.2'N, 83°44.1'W), 12–14 Aug 2001, D. and W.N. Mathis (3♂, 1♀; USNM).

(Fig. 48). Neotropical: Costa Rica (Guanacaste, Limón, Puntarenas).

The species epithet, spinosum, is of Latin derivation and refers to the spinose apical portion of the epandrium.

As implied by its species’ name, spinosum, this species is distinguished from congeners by the numerous spine-like structures on the U-shaped, ventroapical portion of the epandrial process. The angulate, lateral epandrial margins are also distinctive.

This species is distinguished from other congeners by the following combination of characters: Small shore flies, body length 1.25–1.45 mm. Head: Antenna mostly blackish gray; medial surface of basal flagellomere mostly dark colored; parafacial silvery white, concolorous with facial coloration (Figs 49–51); gena-to-eye ratio 0.23–0.25. Thorax: Mesonotum with extensive metallic green coloration, extended laterally to notopleuron and presutural area. Wing with costal vein ratio 0.80–0.82; M vein ratio 0.46–0.48. Forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface; tibiae mostly gray; hindtibia bearing a long, spur-like seta ventroapically. Abdomen: Tergites 1–4 greenish gray, subshiny, lacking wedge-shaped, gray to silvery gray areas, tergite 5 of male more gray colored than preceding tergites. Male terminalia (Figs 52–56): Combined structures generally moderately elongate, in posterior view height slightly more than 3× width, generally sparsely setulose dorsally, bearing large to small setulae ventrally; epandrium with dorsal arch above cerci relatively thinly developed, incompletely connected medially, in posterior view (Fig. 52) as an inverted U on dorsal third with disconnect dorsomedially, thereafter ventrally widest sub-basally, then tapered with lateral margins shallowly curved medially, ventral third as very thin, elongate, digitiform, parallel-sided projections, these cruciate subapically, deeply bifurcate medially, medial bifurcation wider basally than width of ventral projections at same level, ventral epandrial projections minutely setulose, apical setulae stout, apex rounded; cerci moderately long, height nearly twice width, widely semi-hemispherical (Fig. 53), not attached lateroventrally with epandrium; aedeagus in lateral view (Fig. 55) elongate, over 5× longer than wide, tubular, shallowly curved, slightly tapered toward apex with apical portion moderately and irregularly pointed, in ventral view (Fig. 54) nearly straight sided, slightly thinner medially than basally or subapically, apical portion tapered to narrowly rounded apex; phallapodeme in lateral view (Fig. 55) generally narrow to very shallowly and broadly triangular, extended keel only a slight bump toward attachment with hypandrium, in ventral view (Fig. 54) an elongate, thin T with crossbar very short; gonite in lateral view (Fig. 55) narrow, elongate, bar-like, very shallowly curved, in ventral view (Fig. 54) shallowly curved, tapered at both ends; hypandrium in lateral view (Fig. 55) elongate, as long or slightly longer than aedeagus, moderately thin, mostly parallel sided, anterior portion evenly tapered to narrowly rounded anterior apex, in ventral view (Fig. 54) generally as a gently curved arrowhead with posterior half generally narrower, posterior margin widely and moderately deeply emarginate with narrow, lateral arms, tapered to anterior portion of base, anterior portion elongate, V-shaped with lateral margins shallowly curved, with elongate, narrow, lateral, posterior extended processes that are aligned parallel to overall orientation of hypandrium, anterior margin tapered to bluntly rounded apex.

The holotype male of Hydrochasma viridum is labeled “GUYANA. Karanambo[, ] Rupununi Riv[er], ox bow[, ] 3°45.1'N, 59°18.6'W[, ] 2Apr1994, W. Mathis/HOLOTYPE ♂ Hydrochasma viridum Mathis & Zatwarnicki, USNM [red]/USNM ENT 00089395 [plastic bar code label].” The holotype is double mounted (minuten in a block of plastic), is in good condition (some dirt specks on specimen), and is deposited in the USNM. Paratype are as follows: GUYANA. Moco-Moco, Lethem (30 km E in Kanuku Mountains; 03°18.2'N, 59°39.0'W), 3–6 Apr 1994, W. N. Mathis (1♂, 1♀; USNM); Pirara Ranch and River (03°32.1'N, 59°40.5'W), 24–25 Apr 1995, W. N. Mathis (1♂, 1♀; USNM).

Guyana. Karanambo, Rupununi River (ox bow; 03°45.1'N, 59°18.6'W).

(Fig. 56). Neotropical: Guyana.

The species epithet, viridum, is of Latin derivation, meaning green, and refers to the metallic green coloration of the mesonotum.

Externally, the dorsum of the head and mesonotum of this species is unique among congeners, especially species in the faciale group, in having a pronounced, subshiny to shiny, with mostly greenish to bluish luster. Internally, this species could only be confused with Hydrochasma patens, and indeed, structures of the male terminalia of these two species are similar, although differing in details (compare Figs 26–29 with Figs 52–55).

This species is distinguished from congeners by the following combination of characters: Small to moderately small shore flies, body length 1.50–2.30 mm. Head: Subglobose, very broad ventrally, oral opening comparatively large. Antennal coloration variable, entirely yellow to nearly evenly divided between yellowish and dark gray, dorsal and anterior surfaces of pedicel and basal flagellomere extensively dark gray. Parafacial silvery white, concolorous with facial coloration; parafacial silvery white, concolorous with face; mesonotum yellowish to golden brown; gena-to-eye ratio 0.25–0.27. Thorax: Pleural area gray (Fig. 1). Wing with costal vein ratio 0.63–0.65; M vein ratio 0.52–0.53. Forefemur bearing a distinctive, comb-like row of stout setulae along anteroventral and posteroventral surfaces; tibiae mostly gray; hindtibia bearing a large, spur-like seta ventroapically (Fig. 11). Abdomen: Tergites 1–4 with broad, medial brown stripe, uneven lateral margin, lacking wedge-shaped, gray to silvery gray areas laterally (Fig. 1); tergite 5 of male truncate apically, mostly gray with faint brown, medial stripe. Male terminalia (Figs 57–60): Combined structures generally moderately elongate and appearing angulate, in posterior view height about 1.3× width, generally setulose, especially medially at midlength but also along ventral margins; epandrium with dorsal arch above cerci attenuated, not connected, in posterior view (Fig. 57) with cercal cavity forming a broad U, with arms of U robustly developed, ventral portion of arms with each lateral half robustly developed, tapered to dorsal apex, apex pointed medially, dorsal portion of epandrium squarish, especially prominent dorsolateral, rounded angles; ventral portion of epandrium ventrad of midlength, shallow, V-shaped notch, as 2 robust, ventral projections that are tapered to a narrow point ventroapically, forming a deeply and narrowly incised medial incision or narrowly U-shaped pocket, in lateral view (Fig. 58) with very irregular anterior and posterior margins, generally robust, apex narrowly pointed; cerci moderately long, height more than twice width, widely semi-hemispherical (Fig. 57), pointed dorsally, in lateral view (Fig. 58) evenly lunate, not attached lateroventrally or ventrally with epandrium; aedeagus in lateral view (Fig. 60) elongate, length slightly more than 3.5× width, tubular, shallowly curved, especially apically, apex narrowly pointed, in ventral view (Fig. 59) elongate, widest sub-basally, thereafter apically tapered to narrowly truncate apex; phallapodeme in lateral view (Fig. 60) irregularly triangular, short, with extended, medial keel short and narrow, not skewed, apex of keel rounded, in ventral view (Fig. 59) a slightly elongate, moderately robust T with keel portion as a symmetrical, lateral bulge; gonite in lateral view (Fig. 60) moderately narrow, moderately elongate, bar-like, nearly straight, end toward aedeagus tapered to point, in ventral view (Fig. 59) small, width only slightly longer than length, tapered medially; hypandrium in lateral view (Fig. 60) like a deep, globularly rounded pocket, wide, tapered to point posteriorly, anterior margin broadly rounded, in ventral view (Fig. 59) very broadly and robustly developed, width only slightly longer than length, posterior margin very shallowly emarginated, anterior margin broadly rounded.

The holotype male of Hydrochasma williamsae is labeled “BELIZE. Stann Cr[ee]k. Dist[rict]. MullinsRiver[, ] (17km N Dangriga)[, ] 29 March 1988, Wayne N. Mathis/HOLOTYPE ♂ Hydrochasma williamsae Mathis & Zatwarnicki, USNM [red]/USNM ENT 00094378 [plastic bar code label].” The holotype is double mounted (minuten in a block of plastic), is in excellent condition, and is deposited in the USNM. Sixteen paratypes (5♂, 11♀; USNM) bear the same label data as the holotype.

Belize. Stann Creek: Mullins River (17 km N Dangriga; 17°06.2'N, 88°17.8'W).

Nearctic: UNITED STATES. NEW MEXICO. Grant: Mimbres River (32°43.8'N, 107°52'W; 1665 m), 13-22 Aug 2007, 2009, D. and W. N. Mathis, T. Zatwarnicki (2♂; USNM).

TEXAS. Llano: Enchanted Rock (30°30.4'N, 98°49.1'W), 15 Jun 1953, W. W. Wirth (1♂; USNM).

Neotropical. COSTA RICA. Cartago: La Suiza (09°51.5'N, 83°37.5'W), 28 Jun 2001, W. N. Mathis (2♂, 4♀; USNM). Limón: Talamanca (Estación Gandoca; 9°37.4'N, 82°41.7'W), 18 May 2004, W. Porras (1♂; INBIO).

HONDURAS. Cortés: Omoa (16°47.8'N, 87°58.4'W), 26 Sep 1995, D. and W. N. Mathis (1♂, 1♀; USNM).

(Fig. 61). Nearctic: United States (New Mexico, Texas). Neotropical: Belize (Stann Creek), Costa Rica (Cartago, Limón), Honduras (Cortés).

The specific epithet, williamsae, is a genitive patronym to honor our colleague and cherished friend, the late Ms Hollis Barton Williams, who provided technical support to us for nearly 35 years. Holly passed away August 23, 2009.

This species, as noted previously in the “Remarks” section of Hydrochasma faciale, is distinguished by structures of the male terminalia, especially the generally short and robust epandrium in posterior and lateral views. The more angulate dorsolateral shoulders (best seen in posterior view) and the tapered and pointed ventral epandrial process are unique to this species and distinguish it from congeners.

This species is distinguished from congeners by the following combination of characters: Small shore flies, body length 1.15–1.70 mm. Head: Antenna mostly dark gray; parafacial silvery white, concolorous with facial coloration (Figs 62–64); gena-to-eye ratio 0.0.19–0.21. Thorax: Wing with costal vein ratio 0.68–0.71; M vein ratio 0.54–0.56. Forecoxa whitish gray, yellowish at apices; forefemur lacking a distinctive, comb-like row of stout setulae along anteroventral surface; tibiae mostly gray. Abdomen: Tergites 2–3with wedge-shaped silvery-gray areas on slate black dorsum (Fig. 71); tergite 5 of male mostly gray with blackish posterior margin. Male terminalia (Figs 65–68): Combined structures generally moderately elongate, in posterior view height 2.25× width, generally sparsely setulose dorsally, setulae sparse or lacking ventrally; epandrium lacking dorsal arch above cerci, in posterior view (Fig. 65) with apical 1/2–2/3 abruptly narrowed, parallel sided, apical process not wider than apical 1/2, apex with very narrow apicomedial cleft, in lateral view (Fig. 66) very elongate, narrow with basal 3/4 straight, apical 1/3 becoming slightly wider, slightly expanded, apex narrowly rounded, with paired subapical tooth-like structures on each process; aedeagus in lateral view (Fig. 68) very elongate and very narrow, mostly parallel sided, apical 1/8 expanded anteriorly and to a less degree posteriorly, apex irregularly rounded, in ventral view (Fig. 67) very narrow and elongate, apical 1/8 bulbously expanded, apex broadly V-shaped; phallapodeme in lateral view (Fig. 68) very narrow and elongate, rod-like, hypandrial end with narrowly pointed keel, aedeagal end very shallowly curved, in ventral view (Fig. 67) elongate, narrow, truncate, slightly and gradually expanded at aedeagal end, hypandrial end with 2 narrow crossbars; gonite in lateral view (Fig. 68) as a very shallowly curved, rod-like process, about equal in length to phallapodeme, in ventral view (Fig. 67) shallowly curved to straight, tapered at both apices; hypandrium in lateral view (Fig. 68) narrowly developed, anterior half narrowly angled, gradually expanded toward midlength, thereafter narrowed to parallel-sided, elongate extension, in ventral view (Fig. 67) moderately deeply and thickly V-shaped, with base of V rectangular, robustly developed, extended lateral arms thick, elongate, each narrowly cleft apically, bifurcate.

The holotype male of Hydrochasma denticum is labeled “ECUADOR. Prt. Or[e][l]lana: RioTiputini(0°38.2'S, 76°8.9'W), 12–26 Aug 1999, W.N.Mathis, A. Baptista, M. Kotrba/USNM ENT 00117964 [plastic bar code label]/HOLOTYPE ♂ Hydrochasma denticum Mathis & Zatwarnicki, USNM [red].” The holotype is double mounted (minuten in a block of plastic), is in excellent condition, and is deposited in the USNM. Seventeen paratypes (15♂, 2♀; USNM) bear the same label data as the holotype.

Ecuador. Orellana: Río Tiputini (0°38.2'S, 76°8.9'W).

Neotropical. BOLIVIA. El Beni: Cavinas (12°31'S, 66°49'W), Jan 1922, W. M. Mann (2♀; USNM); Huachi (14°13.8'S, 63°32.1'W), 21 Sep, W. M. Mann (13♂, 1♀; ANSP, USNM). La Paz: Guanay (15°29.8'S, 67°52.7'W), 460 m), 13 Mar 2001, W. N. Mathis (2♂; USNM).

HONDURAS. Cortés: San Pedro Sula (8 km S; 15°25.7'N, 88°01.4'W), 25–26 Sep 1995, D. and W. N. Mathis (1♂; USNM).

PERU. Madre de Dios: Río Manu, Pakitza (11°56.6'S, 71°16.9'W; 250 m), 9 Sep 1988, W. N. Mathis (10♂, 15♀; USNM).

(Fig. 69). Neotropical: Bolivia (El Beni, La Paz), Ecuador (Orellana), Honduras (Cortés), Peru (Madre de Dios).

The species epithet, denticum, is of Latin derivation and means tooth, referring to the tooth-like subapical structures toward the apex of the extended epandrium.

As implied by its species’ name, denticum, this species is distinguished from congeners by the paired, tooth-like structures located subapically on each of the ventral epandrial processes. In addition, the hypandrium in ventral view is V-shaped with robust, posterior arms that in turn are bifurcate apically.