Proceratium dusun

Identification
A Proceratium species belonging to the silaceum clade and resembling Proceratium banjaranense, but differing from it, in the worker, by the shorter hairs, by the narrower petiolar node and by the first gastral tergite less convex. Also Similar to Proceratium banjaranense but Proceratium dusun is more sculptured and has a less shining gaster.

Distribution
Known only from Sabah, Malaysia.

This taxon was described from Borneo.

Nomenclature

 *  dusun. Proceratium dusun De Andrade, in Baroni Urbani & De Andrade, 2003b: 385, fig. 149 (w.) BORNEO.

Worker
Head slightly longer than broad and with the sides gently diverging posteriorly. Vertex in full face view gently convex. Clypeus reduced and as long as the antennal sockets. Anterior border of the clypeus truncate. Frontal carinae far from each other and slightly covering the antennal insertions. Lateral expansions of the frontal carinae broad, little raised, diverging on the two anterior fourths, converging on the third fourth, parallel and carinate only on the last fourth. Frontal area gently concave on the three anterior fourths and with a central, thick longitudinal carina starting from the last fourth and prolonging posteriorly. Head anterolaterally with a short, longitudinal carina. Genal carinae marked, each carina corresponding to the external border of a sulcus. Eyes visible as a dark dot below the integument, sinall and on the middle of the head sides. First funicular joint about as long as broad. Funicular joints 2-10 broader than long. Last funicular joint as long as the sum of joints 6-10. Scapes short of the vertexal margin and gently broadened apically. Masticatory margin of the mandibles with 8-10 denticles before the pointed apical tooth. Palp formula 2,2.

Mesosoma in side view weakly convex and shorter than maximum head length (mandibles included). Pronotal and propodeal sutures absent. Basal face of the propodeum declivous posteriorly. Declivous face of the propodeum gently sloping posteriorly. Area between the basal and declivous faces of the propodeum gently concave medially, dorsally feebly carinate and laterally strongly angulate or denticulate. Sides of the declivous face of the propodeum marginate. Propodeal spiracle round and above mid height in lateral view.

Petiole subrectangular and narrower than in banjaranense. Anterior border of the petiole straight and anterolaterally strongly carinate. Ventral process of the petiole large, stout and triangular. Postpetiole in dorsal view with the sides diverging posteriorly. Postpetiolar sternite anteromedially with a marked subtriangular projection, gently convex posteriorly in side view. Constriction between postpetiole and gaster impressed. Gastral tcrgite I about 1/3 longer than the postpeliole and less convex on the curvature than in banjaranense. Remaining gastral tergites and sternites curved ventrally.

Legs slightly short. All tibiae with a pectinate spur. Spurs of fore legs without basal spine. Fore basitarsi longer than the mid ones. Hind basitarsi about 1/3 shorter than hind tibiae. Second tarsomere of hind legs shorter than pretarsus. Pretarsal claws simple. Arolia absent.

Sculpture. Head dorsum rugosopunctate and very sparsely granulate; head sides reticulate rugulose. Mesosoma, petiole and postpetiole granulopunctate with few irregular rugulae on the mesosoma. Gaster smooth on the center of the posterior half; the remaining parts punctate and slightly granulate. Legs punctate.

Body covered by hairs of three types: (1) short, dense, suberect or subdecumbent on the whole body, sparse on the funicular joints; (2) longer than type (1), erect or suberect on the whole body, sparser and shorter than in banjaranense, absent on the antennae; (3) shorter than hair type (1), dense and decumbent on the funicular joints only. In addition the funicular joints bear whitish, thick, appressed, sparse hairs, and the scapes with sparse hairs similar to type (2) but slightly shorter.

Colour. Light ferrugineous with concolour legs.

Measurements in mm and Indices: TL 2.92-3.02; HL 0.68-0.69; HW 0.64-0.66; EL 0.03-0.04; SL 0.44-0.45; WL 0.83-0.84; PeL 0.20-0.22; PeW 0.30-0.32; HFeL 0.49-0.51; HTiL 0.41-0.42; HBaL 0.27-0.29; LS4 0.30-0.32; LT4 0.61-0.64; GI 94.1-95.6; SI 63.7-65.2; IGR 0.49-0.50.

Type Material
Holotype worker from Malaysia labelled: "Sabah: 850 m, Poring Hot springs, Langanan Riv., 14.V.87, Lobl + Burckhardt", in.

Etymology
Dusun is the name of one of the local peoples of Sabah. It is used as a noun in apposition.