Decarthrocerus jeanneli Orchymont, 1948

Perkins, Philip D., 2009, Revisions of the genera Parhydraena Orchymont, Protozantaena Perkins, Decarthrocerus Orchymont, and Parhydraenopsis nomen novum, aquatic and humicolous beetles from Africa and Madagascar, and comparative morphology of the tribe Parhydraenini (Coleoptera: Hydraenidae), Zootaxa 2038, pp. 1-119 : 53-54

Decarthrocerus jeanneli Orchymont, 1948

( Figs. 4, 18, 84, 86, 103)

Decarthrocerus jeanneli Orchymont, 1948: 35

Parhydraena jeanneli (Orchymont) : Perkins, 1997: 205.

Type material. Holotype (male) (not examined): Kenya: Mt. Elgon , Versant Est, Saw Mill (Camp II), 2,470 m. Depository uncertain; original description does not give depository (see notes) . Paratypes examined: Same data as holotype (3 MNHN, 1 MCZ); Same data, except Suam Fishing Hut, 2,400 m (1 MCZ) .

Differential diagnosis. This species is similar in habitus to D. mbizi ; differing therefrom by the less explanate pronotum and elytra and the less convex pronotal relief and elytra, and other subtle differences ( Figs. 84, 88). The male genitalia of the two species differ markedly, and should be examined for reliable determinations ( Figs. 86, 90).

Description. Size (length/width, mm) paratype: body (length to elytral apices) 2.15/0.91; head 0.33/0.61; pronotum 0.50/0.83, PA 0.71, PB 0.64; elytra 1.35/0.91. Color dark brown to piceous; maxillary palpi light brown; dorsum with stiff, arcuate, yellow setae (dorsum usually thickly coated with debris).

Head with eyes small in dorsal aspect, ca. 7 convex facets in longest series. Ocelli evident. Frons markedly concave laterally, hence eyes appearing elevated; cuticle dull, with granule at base of each arcuate seta, granules ca. 1xef. Frontoclypeal suture arcuate, widely U-shaped. Clypeus with setae and granules smaller and denser than those on frons. Labrum dull, set at angle to clypeus, hidden in habitus view, apically emarginate. Maxillary palpi very short, combined lengths of meres much less than width of head (ratio ca. 15/ 43); ratios of meres 2–4 ca. 6/2/7, last mere non-penicillate. Mentum and submentum finely, densely punctulate, very sparsely setose, interstices shining.

Pronotum with anterior margin straight, median 1/3 with narrow hyaline border. Anterior angles obtuse, sharply rounded. Sides coarsely crenulate, rounded, widest at about midlength, behind markedly attenuate, weakly emarginate. Posterior angle obtusangulate. Discal relief prominent, moderately shining, granules oblong, ca. 1xef, separated by ca. 1–3xef, each granule with strong, arcuate seta. Anterior and posterior impressions deep, anterior continuous with impression at each anterior angle; deep, wide impression at each posterior angle. Sculpture laterally slightly less densely granulate than disc, weakly shining.

Elytra moderately shining, sides arcuate, markedly attenuate posteriorly; margins distinct from shoulder for ca. 2/3 of length. Ten-seriate punctate, punctures deep and large, on disc ca. 4xef or larger, separated by less than puncture diameter; each puncture with decumbent seta, no granule at base, setae slightly smaller than interval setae. Intervals shining, width ca. 1–2xpd, each with unilinear row of widely spaced, large, stiff, arcuate setae, similar in size to setae on pronotum.

Metaventrite short, with deep midlongitudinal impression occupying posterior 1/2, strong midlongitudinal carina between anterior extreme of impression and mesoventral intercoxal process. Metaventrite and abdominal ventrites 1–4 with very short hydrofuge pubescence. Apical abdominal segments elongate. Ventrite 5 hydrofuge pubescent in basal 1/5, shining part sparsely pubescent in band across posterior 1/2; ventrite 6 simple, with sparse setae in posterior 1/2; last ventrite symmetrical, apex sharply rounded. Female ventrally similar to male, except apical abdominal segments not elongate, and ventrite 6 weakly apicomedially emarginate.

Legs moderately short, femora stout, tarsi very short, claws small, combined lengths of metatibia and metatarsus shorter than width of head (ratio ca. 37/43), ratio of lengths of metatibia/metatarsus ca. 26/11. Basal 3 tarsomeres setose.

Aedeagus length ca. 0.51 mm; main-piece in ventral view markedly angulate near distal 1/3, then abruptly widened, apex pointed; main-piece in lateral view markedly angulate near midlength, bearing many long setae in slightly widened distal part, apex blunt; complex distal piece small compared to length of aedeagus ( Fig. 8).

Distribution. Currently known only from the type locality at Mt. Elgon, Kenya ( Fig. 103).

Notes. The habitus images and aedeagal illustrations ( Figs. 84, 86) are of a topotypical paratype from Mt. Elgon, Saw Mill. In the original description ( Orchymont, 1948), the depository is not given. I am very grateful to Hélène Perrin ( MNHN), Pol Limbourg (ISBN), and Roger Booth ( BMNH) for making special efforts, unfortunately unsuccessful, to find the holotype in their respective collections .