Medium-sized (TL = 6.9–9.6 mm), elongate, shiny and flattened mainly black diving beetles, unicolorous or with testaceous or ferruginous markings on elytra. Epipleuron in apical half more than twice as wide as base of longer spur of metatibia. Both parameres abruptly narrowed near middle. Outer metatarsal claw curved, prosternum with median furrow. Body covered with dense fine punctures and/or very fine microreticulation, meshes irregular, polygonal.

Allomatus was justified as a genus based only on the presence of a reticulated pronotum and elytra without any punctuation in contrast to Batrachomatus which has a non-reticulate but densely and finely punctate pronotum and elytra (Mouchamps 1964, Watts 1978). Brachomatus larsoni sp. n. has characters from both genera: a polygonal double reticulation with punctures at the intersections of all meshes.

The cox1 sequence data show (Fig. 15) that Allomatus wilsoni is sister to Batrachomatus daemeli, Batrachomatus wingi sister to these two, and Allomatus nannup sister to all of these. We use Matus bicarinatus (Say, 1823) from North America as well as Hygrobia maculata Britton, 1981 and Hygrobia wattsi Hendrich, 2001 as outgroups (Hygrobia were pruned for Fig. 15). Consequently Allomatus Mouchamps, 1964 is here synonymised with Batrachomatus Clark, 1863.

Sydney, New South Wales, Australia.

Lectotype ♂ of Matus daemeli: “Lectotype” [Watts des. 1978: 119], “Type”, “Sydney Austr” [handwritten label], “S.Australia”, “Sharp Coll. 1905-313”, “Type 860 B. Daemeli” [handwritten label], “Batrachomatus daemeli Sydney” [handwritten label], “Matus daemeli Sharp Det. C. Watts 1979” (BMNH). Holotype ♂ of Batrachomatus burnsi: “Macalister River, XI.1946, F.E.Wilson leg”, “Holotype” [red printed label], “Batrachomatus burnsi sp.n. Mouchamps” [handwritten and printed label] (MVMA).

(142 specimens): Queensland: 3 exs., “N QLD, Atherton Tableland, Millaa Millaa Falls, 2500 feet, IV.1932, Australia Harvard Exp. Darlington” (ANIC, SAMA); 1 ex., “S QLD, Brisbane, 1.I.1952, C.Oke leg.” (MVMA). Australian Capital Territory: 1 ex., “Canberra, I.1961, C.H.S. Watts leg.” (SAMA). New South Wales: 4 exs., “N NSW, 20 km NE Tenterfield, Boonoo Boonoo River Cross., 949m, 12.X.2006, 28°52.486S, 152°06.246E, L. & E. Hendrich leg.” (NSW 67) (CLH, ZSM); 21 exs., “N NSW, 35–40 km S Grafton, road [Orara Way] to Coffs Harbour, Flaggy Creek NR, 5m, 15.X.2006, 29.58.587S, 152.58.452E, L. & E. Hendrich leg. (NSW 77)”, one specimen with green printed label “DNA M.Balke 1829” (CLH, ZSM); 6 exs., “C NSW, Glouchestershire, Barrington River at Barrington, 133m, 18.X.2006, 31°58.225S, 151°54.160E, L. & E. Hendrich leg. (NSW 82)”, one specimen with green printed label “DNA M.Balke 1799” (CLH); 8 adults and 14 larvae (LA III), “C NSW, 3 km W Albion Park, North Macquarie Road at creek crossing, 19m, 30.X.2006, 34°34.337S, 150°43.456E, L. & E. Hendrich leg. (NSW 87)” (CLH); 8 exs., “C NSW, Endrick River at Braidwood Road, 554m, 1.XI.2006, 35°05.193S, 150°07.182E, L. & E. Hendrich leg. (NSW 94)” (CLH); 9 ex., “C NSW, 10 km W Braidwood, Shoalhaven River at Bombay Bridge, 628m, 2.XI.2006, 35°25.419S, 149°42.582E, L. & E. Hendrich leg. (NSW 96)” (CLH, ZSM); 4 exs., “S NSW, Wallagaraugh River Picnic Area, 43 km SW Eden, 54m, 17.XI.2006, 37.22.079S 149.43.073E, L. & E. Hendrich leg. (NSW 112)”, four specimens “DNA M.Balke 2371”, “DNA M.Balke 2373”, “DNA M.Balke 2374”, “DNA M.Balke 2375” (CLH, ZSM); 1 ex., “Williams River near Dungog, 27.XI.1996, C.H.S. Watts leg.” (SAMA); 5 exs., “5 km W Bombala, Saucey Creek, 18.I.1997, C.H.S. Watts leg.” (SAMA); 24 exs., “Eccleston, J. Hopson” (ANIC, SAMA); 2 ex., “N NSW, Caparra (Lots 72, 73, 148) 35 km NW Taree, 3.I.1990” (ANIC); 2 exs., “Kindee N.S.W Sept. 1934 H.J. Carter”, “Batrachomatus daemeli Shp. Det. C. Watts 1971”, “K 215108” (AMS); 1 ex., “N NSW, Kindee [Kindee Creek] 50 km W Port Macquarie, IX.1934” (ANIC); 1 ex., “C NSW, Shoalhaven River, 3.I.2001, W.D. Shepard leg.” (ANIC); 1 ex., “C NSW, Wollondilly R. Jooriland, 60 km W Wollongong, 16.XII.1931” (ANIC); 1 ex., “NSW EPA Survey MRHI SHOA (Shoalhaven River System) 01, Kangaroo River and Gerrigong Creek, 26.XI.1997, 34°41.17S, 150°35.58E J. Potts leg. K 227447 Riffle” (AMS); 1 ex., “NSW EPA Survey MRHI CLYD (Clyde River System) 13 d/s, Bimberamala River, 25.X.1995, 35°25.59S, 150°11.36E, A. Leask leg. EPA 08191 Edge” (AMS); 1 ex., “NSW EPA Survey MRHI SHOA 08 (Shoalhaven River System), Upper Corang River, 22.XI.1995, 35°12.19S, 150°03.24E, J. King leg., K 227320, edge” (AMS); 1 ex., “NSW EPA Survey MRHI HAST (Hastings River) 10 Forbes River: Round Flat, 2.X.1994, 31°20.20S, 152°20.23E, E. Turak leg., EPA 10992, logs” (AMS);8 exs., “S NSW, Albury, 16.VII.1989, P. Walker leg.” (SAMA). Victoria: “6 exs., E VIC, Thurra River at Hwy 1, Water Point Rest Area, 138m, 5.XI.2001, 37°34.061S, 149°16.338E, G.L.Challet leg.” (CGC, ZSM); 5 exs., “C VIC, Hughes Creek at Avenel, 161m, 25.XI.2006, 36°54.221S, 145°14.191E, L. & E. Hendrich leg. (VIC 120)”, one specimen with green, printed label “DNA M.Balke 2763”, “DNA M.Balke 2764”, “DNA M.Balke 2765” (CLH); 1 ex., “Western District Lakes Surv 78, 16.I.1980, W.D.Williams leg.” (SAMA); 1 ex., “Tamao Crossing, 24.I.1960, A.Neboiss leg.” (MVMA); 2 exs., “Maffra, I.1939, F.E.Wilson leg.” (MVMA). Tasmania: 1 ex., “Deloraine, Deloraine River, I.1961, C.H.S.Watts leg.” (SAMA).

Measurements. TL = 7.9–9.1 mm, TL-H = 7.3–8.2 mm; MW = 4.0–4.6 mm.

Colour. Dorsal surface shiny, head, pronotum and elytra black, legs dark reddish, antennae and palpi reddish pale. Some specimens with reddish basal markings on elytra (Figs 1, 2, 3).

Structure and sculpture. Body outline oblong oval. Dorsal surface densely and evenly covered with small punctures, and with a very fine, almost subobsolete close reticulation with large meshes. Serial punctures on elytron distinct, large and shallow. Ventral surface finely and densely punctate. Prothoracic process broad, flat, apex pointed, broadly grooved in middle for whole length, sides strongly margined. Metacoxal lines raised, well separated, reaching almost to hind margin of metaventrite, diverging a little anteriorly.

Male. Pro- and mesotarsi dilated and stouter than in female, furnished beneath with dense, short, stout setae arranged in groups, many of the setae ending in minute suction cups. Aedeagus: median lobe in lateral (Figs 8a) and in ventral view (Figs 8b); paramere (Fig. 8c).

Variability. A very variable species in size and colour. Specimens having reddish shoulders of various form and extension were named Batrachomatus burnsi Mouchamps, 1964 (Fig. 2, large red patch on the shoulder) and Batrachomatus burnsi var. obscurior (smaller and interrupted reddish patch on shoulder). Such specimens can be found all over the species distributional range.

According to our study of the complete material of Batrachomatus daemeli two different forms can be recognized: larger specimens (see measurements above) with larger median lobes and smaller specimens [Measurements: TL = 7.3–8.0 mm, TL-H = 6.5–7.05 mm; MW = 3.6–3.9 mm] (Fig. 3) with smaller and less elongated median lobes. The latter have been collected at several places in New South Wales and Victoria, sometimes syntopic with the larger form. Despite the fact that intergrades between the typical Batrachomatus daemeli and the “smaller form” have been found, for some time we even have been strongly tempted to describe those smaller specimens as another new species. On the other hand we have not been able to find any constant extern morphological character—except of the size—and also the shapes of the male genitalia are more or less the same. In addition, in our cox1 tree (Fig. 15) specimens of both forms aregrouped in the same clade.

Batrachomatus daemeli differs from the northern Australian Batrachomatus larsoni sp. n. and Batrachomatus wingii in the broader, more oblong shape, the lack of colour pattern on upper surface in most specimens, the weakly diverging metacoxal lines and the shape of the median lobe.

The most widespread and common species of the genus in Australia (Fig. 13). From the Atherton Tableland in Queensland along the east coast of New South Wales, Canberra area, to western Victoria and north-eastern Tasmania (Watts 1978).

Batrachomatus daemeli inhabits permanent streams, creeks and slow flowing larger rivers at an altitude from about sea level to almost 1000 m, from more or less open country in cultivated areas to closed-canopy forest sites (Figs 20–23). Most specimens were found in low-gradient stream or river sections where the substrate was enriched with rotten leaves, wood and larger stones. In this habitat the beetles were found in areas of medium, laminar flow, generally in deeper water (50 cm depth and more) under larger logs and stones. When disturbed the adults can be observed swimming around and coming to the surface. In dryer periods the species can be found in the deepest parts of the remaining rest pools of a creek or river. All the mentioned smaller specimens from Coffs Harbour, Flaggy Creek were collected in a peaty and intermittent creek, with muddy bottom, shaded by wet eucalypt forest. The adults were mainly being located in a mixture of water and mud under a larger rotten tree trunk (Fig. 20). At this site Batrachomatus daemeli was associated with the rarely collected Sternopriscus wallumphilia Hendrich & Watts, 2004, a dytiscid known before only from its type locality, a single creek in the Wallum heath near Glasshouse Mountains in southern Queensland (Hendrich and Watts 2004). In New South Wales the larvae of Batrachomatus daemeli were collected together with the adults in October and November. Adults can be found all over the year.

Creek, Windsor Tableland access road [16°13'55"S, 145°1'27"E], Queensland, Australia.

Holotype ♂: “AUSTRALIA, QLD Windsor Tableland access rd km 40 Nov. 12/90 Larson” [white printed label], “Holotype Batrachomatus larsoni sp.n. Hendrich & Balke des. 2010” [red printed label] (ANIC). Paratype ♀ with same data as holotype (ANIC). The single paratype is provided with a red printed paratype label.

Measurements. Holotype: TL = 7.9 mm, TL-H = 7.1 mm; MW = 3.85 mm. Paratype: TL = 7.7 mm, TL-H = 7.0 mm; MW = 3.8 mm.

Colour. Dorsal surface shiny, black, appendages reddish.Head black with epistome and labrum lighter. Pronotum with reddish broad lateral margin. Elytron with narrow reddish band along 2/3 of length of elytron (Fig. 4).

Structure and sculpture. Body outline oblong oval, only slightly convex. Head, pronotal and elytral surface covered by polygonal double reticulation, smaller superficial meshes inside larger and more visible meshes, with punctures at intersections of all the larger meshes. Sides of pronotum moderately curved and convergent anteriorly. Sculpture on elytra as in pronotum but punctures at the intersections of all larger meshes smaller. Serial punctures on elytron distinct, large and shallow. On ventral side, metacoxal plate with very fine microreticulation, meshes very elongate, inside minutely and sparsely punctate. Lateral wings of metaventrite very narrow. Prosternal process flat, broad, broadly carinate in midline, parallel-sided, weakly pointed apically, weakly margined. Metacoxal lines well separated, strongly diverging anteriorly. Area between metacoxal lines with many small punctures.

Male. Pro- and mesotarsus a little dilated, basal 3 tarsomeres with dense short setae beneath suction cups. Aedeagus: median lobe (Fig. 9a, b); paramere (Fig. 9c).

This species is dedicated to our Canadian colleague David Larson (Maple Creek, Canada) who collected the only known specimens and recognized the species as new. The specific epithet is a substantive in the genitive case.

Batrachomatus larsoni sp. n. differs from Batrachomatus wilsoni by its smaller size (Batrachomatus larsoni TL = 7.9 mmand Batrachomatus wilsoni TL = 8.4–8.5 mm), in the lack of any reddish humeral angles on elytra, the more flattened and narrowly formed body, and in having the reticulation on the elytra weak without punctuation, instead of moderately strong and punctate. Both species can be separated by the shape of their median lobes.

Only known from the type locality in NE Queensland (Fig. 14).

The Windsor Tableland is a granite plateau at about 1100 m, near to but further inland from Mt. Spurgeon and Mt. Lewis, in north-east Queensland. Because of its altitude, it receives enough rainfall to sustain mountain rainforest over much of the plateau surface, although it is surrounded by tropical eucalypt savannah at lower altitudes. Access to the Windsor Tableland is now for scientific study only, the public are permanently barred. A very detailed habitat description is given by Larson (1993): “Two specimens were collected from a low gradient section of a small, permanent, closed forest stream. The stream was largely shaded by a tall, more or less closed tree canopy. The stream bed was coarse sand and consisted of shallow, gentle riffles which separated pools formed where sand had been scoured from around and behind logs and from under tree roots to produce pools under overhanging roots-mats. The specimens were found swimming in a pool after the trailing roots on an overhanging bank on one side of the pool had been vigorously swept with a net. It is assumed the beetles came from under the bank but similar habitat, which was common along the stream, was searched without yielding additional specimens”.

Bridgetown [Blackwood River, 33°58'02"S, 116°07'58"E], Western Australia, Australia.

Holotype ♂: “Bridgetown Nov 8 31 W.A.” [handwritten label], “Australia Harvard Exp. Darlington” [printed label], “Holotype Allomatus nannup Det. C. Watts 1976” [handwritten and printed label] (ANIC). Paratype ♂: “Bridgetown Nov 8 31 W.A.” [handwritten label], “Australia Harvard Exp. Darlington” [printed label], “Paratype Allomatus nannup Det. C. Watts 1976” [handwritten and printed label], “SAMA Database No. 25-006714” [printed label] (SAMA).

(178 specimens): Western Australia: 2 exs., “Nannup-Balingup Road, Blackwood River, 28.IX.1965, E.B. Britton leg.” (ANIC); 57 exs., “Blackwood River near Nannup, 20.X.1996, C.H.S. Watts” (SAMA); 8 exs., “Blackwood River near Nannup, 20.IX.2000, C.H.S. Watts” (SAMA); 1 ex., “Blackwood River near Bridgetown, 21.IX.2000, C.H.S. Watts” (SAMA); 20 exs., “Nannup, Balingup-Nannup Road, Blackwood River at Revelly Bridge, 79m, 33.55.226S, 115.48.549E, 25.XI.1996, L. Hendrich leg. (Lok. 33)” (CLH, ZSM); 65 exs., “Blackwood River, 8.3 Km NE Nannup, Revelly Bridge, 79m, 6.I.2007, 33.55.226S, 115.48.549E, L. & E. Hendrich leg. (WA 166)”, four specimens provided with green printed labels “DNA M.Balke 1712”, “DNA M.Balke 1713”, “DNA M.Balke 2771”, “DNA M.Balke 2772” (BMNH, NMW, ZSM); 25 exs., “Nannup, Balingup-Nannup Road, Revelly Bridge, 79m, 31.XII.1999, 33.55.226S, 115.48.549E, Hendrich leg. (Loc. WA 6/153)” (CLH, ZSM).

Measurements. TL = 9.1–9.6 mm, TL-H = 8.2–8.6 mm; MW = 4.0–4.3 mm.

Colour. Dorsal surface shiny, black; appendages reddish. Head black with epistome and labrum lighter (Fig. 5).

Structure and sculpture. Body outline narrowly oval, flattened and only slightly convex, pointed apically. Head with strongly impressed reticulation, meshes moderately large and irregular, some scattered small punctures; reticulation and punctures in pronotum rather weak. Elytron with fine reticulation, with transversely elongate small meshes, virtually impunctate apart from serial punctures, being comparatively large and well marked.

Ventral side with metacoxal plate covered by very fine microreticulation, meshes very elongate, inside minutely and sparsely provided with small punctures. Prosternal process flat, broad, broadly carinate in midline, parallel-sided, weakly pointed apically, weakly margined. Metacoxal lines well separated, subparallel in anterior 2/3, moderately diverging posteriad, area between lines with many small punctures.

Male. Pro- and mesotarsi a little dilated, basal 3 tarsomeres with dense short setae beneath suction cups. Aedeagus: median lobe (Fig. 10 a, b); paramere (Fig. 10 c).

Batrachomatus nannup differs from most specimens of Batrachomatus wilsoni and Batrachomatus larsoni sp. n. in the lack of any reddish humeral angles to elytra, the more flattened and narrowly formed body, and in having the reticulation on the elytra weak without punctuation, instead of moderately strong and punctuate. All three species can be easily separated by the shape of their median lobes and their distribution.

An endemic species of the Blackwood River in south-western Australia. All records between Bridgetown and Nannup but probably more widespread in the Blackwood River and its larger tributaries (Fig. 13).

The Blackwood River is the largest river in south-western Australia. The river begins near Quelarup and runs in a south-western direction through the town of Bridgetown then through Nannup until it discharges into the Southern Ocean at Hardy Inlet near the town of Augusta. The river has 41 tributaries and the upper or larger catchment area of the river is in agricultural areas, while the middle catchment area passes through forested areas, and the lower portion of the river passes into mixed forest, agricultural and residential lands (Wikipedia).

At the sampling localities the Blackwood is partly shaded by old River gum trees. In late spring the adults of Batrachomatus nannup can be either found in larger (6–10 m²) and deeper (40–80 cm depth) sandy pools in the floodzone of the river or among floating roots, rotten twigs and logs in shallow water of protected embayments of the slow flowing river (Fig. 16). In summer and in dryer periods the adults were collected only in the deepest parts of the almost standing river, under larger logs, stones and rotten debris (Fig. 17). When disturbed the beetles can be observed swimming around and coming to the surface.

Kerrisdale [King Parrot Creek, 165 m, 37°8'8"S, 145°15'36"E], Victoria, Australia.

Holotype ♂: Not seen. Paratype ♂: “Macalister Riv 11/46 Vic F.E.Wilson”, “Wilson Coll” [handwritten label by Mouchamps], “Paratype” [red, printed label], “Paratype 3804” [blue printed label], “R.Mouchamps det., Allomatus wilsoni nsp.” [handwritten, white label by Mouchamps] (MVMA).

(2 specimens): New South Wales: 1 ex., “S NSW, Wallagaraugh River Picnic Area, 43 km SW Eden, 54m, 17.XI.2006, 37.22.079S 149.43.073E, L. & E. Hendrich leg. (NSW 112)”, “DNA M.Balke 2372” [green printed label] (ZSM). Victoria: 1 ex., “E VIC, Thurra River at Hwy 1, Water Point Rest Area, 138m, 17.XI.2006, 37.34.061S, 149.16.338E, L. & E. Hendrich leg. (VIC 114)” (CLH).

Measurements. TL = 8.4–8.5 mm, TL-H = 7.5–7.7 mm; MW = 4.0–4.15 mm.

Colour. Head black with epistome and labrum lighter. Palpi and antennae brownish. Pronotum entirely black, slightly lighter at margins. Elytra completely black or with more or less developed brownish humeral patch. Ventral side black, appendages lighter with tarsi reddish brown (Fig. 6).

Structure and sculpture. Body outline oval, large, slightly convex. Head with anterior border of epistome a little excavated, not bordered. Head and pronotum surface covered by polygonal double reticulation, smaller superficial meshes inside bigger meshes, with punctures at intersections of all bigger meshes. Sides of pronotum moderately curved and convergent anteriorly. Sculpture on elytra consisting of a weak double reticulation, meshes polygonal, large, smaller and very fine punctures at intersections of very few meshes. Serial punctures on elytra distinct, large and shallow. Ventral surface covered with weakly defined reticulation, meshes, very elongate and more or less oblique or transverse. Prosternal process flat and excavated in anterior midline by median groove. Lateral borders of prosternal process clearly raised. Lateral wings of metaventrite narrow. Metacoxal lines separating metacoxal plate into three unequal parts; the median sparsely punctured, the lateral and the intralinear space almost smooth with an extremely sparse and scarcely visible microreticulation.

Male. Pro- and mesotarsi dilated and stouter than in female, furnished beneath with dense, short, stout setae arranged in groups, many of the setae ending in minute suction cups. Aedeagus: median lobe (Fig. 11 a, b); paramere (Fig. 11 c).

Batrachomatus wilsoni isin body outline and coloration very near to Batrachomatus daemeli but can be easily separated by the presence of a superficial polygonal double reticulation on pronotum and elytra. Batrachomatus wilsoni differs from Batrachomatus larsoni sp. n. by its larger size (Batrachomatus wilsoni TL = 8.4–8.5 mm and Batrachomatus larsoni TL = 7.9 mm), the different elytral coloration, and the more oblong and less narrowly formed body. Furthermore, all three species can be separated by the shape of their median lobes.

South-eastern Australia (Fig. 13). A rarely collected species with a very limited distribution. Only known from four sites from southern New South Wales (Wallagaraugh River) to southern and south-eastern Victoria (Macalister River, King Parrot Creek, Thurra River).

Batrachomatus wilsoni inhabits permanent slow flowing larger rivers, at an altitude from about sea level to almost 170 m, in closed-canopy old growth forest sites. The type locality King Parrot Creek, near Kerrisdale, is in many parts a low gradient river, similar to the south-western Australian Blackwood River. The two recently collected specimens from Victoria and New South Wales were found in low-gradient river sections where the substrate was enriched with rotten leaves, wood and larger stones (Figs 18, 19). In this habitat the beetles were found in areas of medium, laminar flow, generally in deeper water (50 cm and more) under larger logs and stones, always together with numerous Batrachomatus daemeli.

Northeast coast of Australia.

♂: “N. Holl NE Aust 4412” [handwritten label], “Holotype”, “Batrachomatus wingi” [sic!], [blue handwritten label by Clark] (BMNH).

l (71 specimens). Western Australia: 1 ex., “Pilbara Region, De Grey River at Yarrie Station, 10.VII.1953, N.B.Tindale leg.” (SAMA); 1 ex., “East Kimberley, Mitchell Plateau, Surveyors Pool, 150m, 17.VI.1999, Hendrich leg.” (CLH). Northern Territory: 18 exs., “Kakadu N.P., Gungurul Lookout, 50 m, 13.59.359S, 132.19.904E, 1.XI.1996, L. Hendrich leg. (Lok.11)” (CLH); 3 exs., “Finnis River, 10 km W Batchelor, 43m, 20.VIII.2006, 13.01.278S, 130.57.217E, L. & E. Hendrich leg.” (NT 2), provided with green printed labels “DNA M.Balke 2773”, “DNA M.Balke 2774”, “DNA M.Balke 2775” (ZSM, CLH); 4 exs., “Kakadu NP, Gunlom Waterfall Area, 72m, 25.VIII.2006, 13.26.026S, 132.25.141E, L. & E. Hendrich leg.” (NT 17), one specimen with green printed label “DNA M.Balke 1659” (ZSM); 20 exs., “Magela Creek upstream, Jabiru East, 38m, 29.VIII.2006, 12.40.458S, 132.55.853E, L. & E. Hendrich leg.” (NT 21) (CLH, NMW, ZSM); 1 ex., “Magela Creek downstream, Jabiru East, 31m, 30.VIII.2006, 12.38.312S, 132.53.441E, L. & E. Hendrich leg. (NT 23)”, “DNA M.Balke 2772” [green printed label] (ZSM); 1 ex., “Daly River, H. Wesselmann” (SAMA); 4 exs., “Kakadu N.P., Jim Jim District, Jim Jim Falls Camping Area, Jim Jim Creek, 60 m, 13.16.218S, 132.49.276E, low-gradient stream, 26. & 27.X.1996, Hendrich leg./loc. 2a” (CLH);1 ex., “Kakadu N.P., Mary River District, 3 km ESE Gunlom Camping Area, South Alligator River, 50m, 2.XI.1996, 13.27.276S, 132.26.268E, L. Hendrich leg.” (loc. 14) (CLH); 1 ex., “Fergusson River, 31 km SE by S of Pine Creek, 14.XI.1979, T.A.Weir leg.” (ANIC). Queensland: 6 exs., “Foleyvale Aboriginal Reserve, 130 km W Rockhampton, 20.–25.I.1968, G. Hangay leg.” (HNHM, CLH); 4 exs., “Boolburra, 95 km WSW Rockhampton, 12.I.1968, G. Hangay leg.” (HNHM, CLH); 1 ex., “N Queensland, Bridge Creek, 20.XI.1992, water sweep, A. Calder & P. Zborowski leg.” (ANIC); 1 ex., “N Queensland, Kennedy River Xing, dry river bed, sandy base, temporary pool, 16.VI.1992, T.A. Weir leg.” (ANIC). Without any detailed locality label: 4 exs., “Australien”, “Sammlung Clemens Müller”, “Sammlung Zimmermann” (ZSM).

Literature records: Australia, Western Australia, Weaber Plain, Keep River east of Milligans, 15°37'11"S, 129°02'00"E, May 2009, A.W. Storey leg. (WRM 2010); Australia, Northern Territory, Sandy Creek downstream of Keep River at Legune Road Crossing, 23.VII.–1.VIII.2004, 15°22'54"S, 129°11'43"E, A.W. Storey leg., site code SE 1, idem, Sandy Creek upstream of Keep River Road, 23.VII.–1.VIII.2004, 15°24'30"S, 129°11'33"E, A.W. Storey leg., site code SR 2 (NCTWR 2005).

Measurements. TL = 6.9–7.8 mm, TL-H = 6.2–7.2 mm; MW = 3.2–3.7 mm.

Colour. Black, anterior part of head reddish brown, pronotum with broad yellow lateral margins, elytron with a narrow yellow band of which apical 1/3 close to side and basal 2/3 some distance from side (Fig. 7). Underside and parts of head reddish brown, appendages reddish brown.

Structure and sculpture. Body outline elongate oval, flattened, pointed apically. Dorsal surface shiny, head, pronotum and elytral surface densely and evenly covered with small punctures, reticulation absent. Serial punctures on elytron sparse, weakly impressed, indistinct. Sides of pronotum moderately curved and convergent anteriorly. Ventral surface very densely and minutely punctured. Prosternal process flat, broad, parallel-sided, weakly and narrowly grooved in midline, and weakly margined at side, tip bluntly pointed, apex pointed. Metacoxal lines well separated, subparallel, reaching almost to hind margin of metaventrite.

Male. Pro- and mesotarsi stouter than in female, furnished beneath with dense, short, stout setae arranged in groups, many of the setae ending in minute suction cups. Aedeagus: median lobe (Fig. 12 a, b); paramere (Fig. 12 c).

A very characteristic species and one of the most beautiful dytiscids in Australia (Fig. 7). Batrachomatus wingii differs from all other species of the genus in the narrower and more flattened shape of body, the dorsal yellowish longitudinal stripes on the elytra, the subparallel metacoxal lines and the shape of the median lobe.

Tropical northern Australia. Occurring from the northern Pilbara and the Kimberley region in the northwest, the Daly River, Darwin area and Kakadu National Park in the north, to the Atherton Tableland in northern Queensland, and along the east coast south to Rockhampton (Fig. 14).

Batrachomatus wingii occurs in seasonal and permanent lowland streams, creeks and slow flowing smaller rivers at an altitude from about 20 to almost 150 m, at least partly shaded by eucalypt woodland or monsoonal forest. Most specimens were found in low-gradient stream sections where the substratum was entirely coarse sand and smaller pebbles yet the current was strong enough to clear the bottom of silt and leaves (Figs 24, 25, 27). In this habitat the beetles were found in areas of medium, laminar flow, generally in deeper water (50 cm depth and more), along the outside curve of stream bend, among floating gum roots, under larger logs and stones. In the Northern Territory, at the end of the dry season, a larger series of the species was collected in the deepest, coldest and most oxygen rich part (50–80 cm depths) of a rest pool (10 m²), situated in a broad and almost dry and sandy creek bed. The pool was without any vegetation but rich in rotten leaves and partly shaded (Fig. 26). As mentioned by Larson (1993), who collected the species in northern Queensland at three different sites, the sub-surface seepage and local water temperatures could also be factors responsible for the local aggregation of beetles. In the Northern Territory larvae have been collected after the rainy season in February by Watts (Alarie et al. 2001).