♀, Saudi Arabia, Riyadh, Al Amariah, [Mazra’ah] Majra Al-Gasim [farm], 23-v-2011 [23 May 2011], M.A. Hannan // at flowers of Blepharis ciliaris [(L.) Acanthaceae] (KSMA).

1♂, 1♀, with the same data as the holotype (SEMC); 2♂♂, same data as holotype except 31-v-2011 [31 May 2011], I. Naser // at Blepharis ciliaris (SEMC & KSMA); 1♂, same data as holotype (KSMA); 1♂, same data as holotype except 17-v-2011 [17 May 2011] (KSMA).

The female of this species can be recognized easily by the following combination of characters: body light reddish brown contrasting with dense, minutely-branched white setae on the body (Figs 1, 2); preoccipital border distinctly concave in dorsal view; clypeus, supraclypeal area, frons, and upper paraocular area with modified facial setae; and clypeus with distal margin distinctly impunctate and swollen medially (Figs 4, 5). In addition to the body coloration and pubescence (Figs 7, 8), which are similar to those of the female, the male can be recognized by the following combination of characters: clypeus distinctly pointed on distal margin (Fig. 10); mandible without inferior process; tarsi of all legs unmodified but with small dark spot on inner surface of probasitarsus; sixth metasomal tergum horizontal in profile, and seventh tergum with strong, transverse preapical carina deeply notched medially (Fig. 12).

The reddish body coloration contrasting with the white dense pubescence of Chalicodoma riyadhense resemble some Palearctic and Oriental species, such as Chalicodoma flavipes (Spinola), Chalicodoma rubripes (Morawitz), and Chalicodoma xanthocneme (Alfken), but it is easily separated from those and any other known species of Pseudomegachile, including those with modified facial setae, by the distinctive clypeus in both sexes. Furthermore, the male of Chalicodoma riyadhense is also unique in having a seventh metasomal tergum with strong, medially notched preapical carina. Except for some species, such as Chalicodoma kigonserana (Friese) and Chalicodoma nigrocaudata (Friese), most Pseudomegachile males have a seventh tergum with a complete or medially pointed preapical carina. However, those males with similar bilobed preapical carina are much larger in size (18‒20 mm in body length), have very long procoxal spines, strongly modified protarsi, and a different color pattern of the pubescence (head and mesosoma covered with black setae contrasting with ferruginous setae on the metasoma).

Female. Body length 10.4 mm; forewing length (measured from apex of humeral sclerite to wing margin) 6.4 mm. Head 1.1 times broader than long; inner orbits of compound eyes parallel-sided; intertorular distance 2.2 times torulorbital distance; interocellar distance 3.2 times median ocellar diameter, 1.7 times ocellocular distance; ocelloccipital distance 1.7 times median ocellar diameter; torular process reduced, barely visible; vertex rounded in frontal view (Fig. 3); preoccipital border rounded, distinctly concave in dorsal view (Fig. 2); compound eye about 2.3 times longer than wide; gena slightly narrower (0.8x) than compound eye in profile, narrowest dorsally; mandible with four teeth, apical two longer and broader than basal two (Fig. 5); clypeus about 1.7 times broader than long, with epistomal sulcus gently convex basally, well projected over clypeal-labral articulation, elevated along midline on disc, distinctly swollen on distal margin medially (Figs 4, 5); supraclypeal area slightly elevated along midline; frons convex in profile, not flat; scape about 3 times longer than broad, not reaching lower margin of median ocellus in repose, pedicel about as long as broad, first flagellomere about as long as broad, about equal to pedicel length, 1.5 times longer than second flagellomere, subsequent flagellomeres progressively increasing in length towards apical flagellomeres, distalmost flagellomere longest. Omaulus rounded; pronotal lobe carinate; mesoscutum gently convex in profile; mesoscutellum flat on disc; pretarsal claws simple, basally with two unmodified simple setae, basal seta shortest; pro- and mesotibiae distally with angled medial projection on outer surfaces, not forming distinct spinose process. Second to fifth metasomal terga with elevated discal areas (i.e., premarginal lines distinct); sixth tergum straight in profile.

Body color light reddish brown except dark brown to black as follows: mandible distally, clypeal margin, epistomal sulcus, vertex, antenna (darker on outer surfaces of scape and pedicel), and mesoscutum and mesocutellum with faint spots on discs (Figs 2, 6). Tegula and humeral sclerite yellowish; wings hyaline, darker distally, veins yellowish basally (including pterostigma), dark brown distally.

Integument smooth and shiny between punctures except strongly imbricate on basal area of propodeum and weakly imbricate on metasomal sterna and terga. Face finely and closely punctate, nearly contiguous except on distal margin of clypeus medially smooth and shiny, punctures smaller on supraclypeal area; gena with shallower punctures than on face. Mesoscutum and mesoscutellum with punctures coarser and larger than on head (Fig. 6), those on mesoscutellum larger than on mesoscutum; mesepisternum with larger and coarser punctures than on metepisternum and sides of propodeum, punctures shallow on metepisternum; basal area of propodeum weakly striate basally. Metasomal terga finely punctate, punctures not contiguous, smaller than on mesoscutum; sterna with punctures coarser, sparser than on terga.

Pubescence white, unless indicated otherwise. Following areas with dense (integument obscured or barely visible among setae), minutely-branched, appressed or semierect setae: mandible basally, lower and middle paraocular areas, gena, pronotum, pronotal lobe, anterior half of tegula, humeral sclerite, margins of mesoscutum, mesoscutellum, metanotum, propodeum, remaining areas of mesosoma laterally, coxae, trochanters, posterior surfaces of pro- and mesofemora, anterior surface of metatibia, outer surfaces of tibiae, outer surfaces of pro- and mesobasitarsi, first metasomal tergum entirely, depressed marginal areas of second to fourth terga (apical fasciae), fifth tergum entirely, distal margin of first sternum, sides of second to fourth sterna, and entire distal margin of fifth sternum; setae longer on head and mesosoma than on metasoma (Figs 1, 2). Clypeus, supraclypeal area, frons, and upper paraocular area with simple, stiff, apically-curved yellowish setae (at most as long as median ocellar diameter) sparsely covering integument (Fig. 3). Lower margin of mandible and gena inferiorly with long (about two times median ocellar diameter), erect, yellowish simple setae. Second to sixth metasomal sterna with yellowish scopal setae, shorter on sixth sternum.

Male. As described for female except for usual secondary sexual characters and following: Body length 11.6 mm; forewing length 6.4 mm. Head 1.2 times broader than long; inner orbits of compound eyes slightly converging below; intertorular distance 1.8 times torulorbital distance; interocellar distance 2.1 times median ocellar diameter, 1.8 times ocellocular distance; ocelloccipital distance 1.4 times median ocellar diameter; vertex slightly flat medially in frontal view (Fig. 9); preoccipital border not as distinctly concave as in female; compound eye about 2.6 times longer than wide; mandible with four teeth, without inferior process; clypeus more convex than in female, with distal margin distinctly projecting over clypeal-labral articulation, so that triangular in ventral view; scape 2.7 times longer than broad, reaching lower margin of median ocellus in repose, second to eleventh flagellomeres longer than broad. Procoxal spine small, about half length of median ocellar diameter as measured in profile; tarsi of all legs unmodified, but probasitarsus with inner surface asetose, with small dark spot; pretarsal claws cleft, inner ramus shorter than outer. Sixth metasomal tergum horizontal or nearly so in profile, without lateral projection on distal margin, transverse preapical carina strong, irregularly toothed, with broad median emargination (Fig. 11); seventh tergum with transverse preapical carina strongly projected, with deep median emargination thus forming a distinct lateral lobe (Fig. 12); fifth to eighth sterna (seventh sternum obsolescent in Megachilini) and genital capsule as in figures 13–17; volsella with apex distinctly notched or bilobed.

Body color slightly lighter than female but with frons, vertex, gena dorsally, mesoscutum, and mesoscutellum black (Figs 7, 8).

Pubescence in general longer and denser than female, particularly on discs of mesoscutum, mesoscutellum, and metasomal terga; clypeus, supraclypeal area, paraocular area, and frons densely covered by setae (integument obscured); procoxa with dense patch of short ferruginous setae above spine, coxa otherwise sparsely covered with branched setae. Fifth metasomal sternum with spatulate setae midbasally on postgradular area, setae otherwise minutely branched, except apicolaterally with long, simple setae; sixth sternum with dense spatulate setae basolaterally on postgradular area forming distinctive patch, otherwise setae apically flattened and curved; sternum eight without setae on or near lateral margin but ventrally with dense, minutely-branched setae on disc (Fig. 15).

The specific epithet refers to the greater Riyadh area in Saudi Arabia, and from where the species was collected.

The species was captured visiting flowers of Blepharis ciliaris (L.) (Acanthaceae), locally known as “Saha” or “Naqie” (Figs 18–20). The plant is a perennial herb, usually about 20 cm in height (10–30 cm), growing in small patches with small blue to light violet flowers and easily found in the area of Al Amariah, approximately 25 km northwest of Riyadh, from early April through early June. The species prefers the silt bottoms of rocky wadi basins. Blepharis ciliaris is a good source of nectar, particularly in the southwest and in years following a good rainy season. Regional beekeepers sometimes produce “Saha honey”.