Proceratium siamense

Identification
A member of the silaceum clade, resembling Proceratium australe in general body shape. The two species Proceratium siamense and australe share the area between the basal and declivous faces of the propodeum with a variably marked transversal carina. Differing from australe, in the worker, by the thicker petiole and by the hairs of type 2 denser and longer. (Baroni Urbani and de Andrade 2003)

Distribution
This taxon was described, and is only known, from Thailand.

Nomenclature

 *  siamense. Proceratium siamense De Andrade, in Baroni Urbani & De Andrade, 2003b: 342, fig. 136 (w.) THAILAND.

Worker
Head longer than broad and with the sides gently diverging posteriorly. Vertex in full face view slightly convex. Clypeus reduced and as long as the antennal sockets. Anterior border of the clypeus truncate. Frontal carinae not very far from each other, slightly covering the antennal insertions. Lateral expansions of the frontal carinae narrow, little raised, strongly diverging on the two anterior fourths, converging on the third fourth, subparallel and carinate only on the last fourth. Frontal area gently concave on the three anterior fourths and with a central longitudinal carina starting from the last fourth and prolonging posteriorly. Head anterolaterally with a thick, short, longitudinal carina. Genal carinae marked, each carina corresponding to the external border of a deep sulcus. Eyes visible as a dark dot below the integument, small 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 7-10. Scapes short of the vertexal margin and weakly thickening apically. Masticatory margin of the mandibles with 6-7 denticles before the pointed apical tooth. Palp formula 2,2.

Mesosoma in side view gently convex and about as long as the maximum head length (mandibles included). Pronotal and propodeal sutures absent. Basal face of the propodeum declivous posteriorly. Declivous face of the propodeum almost perpendicular to the basal face. Area between basal and declivous faces of the propodeum medially weakly concave, dorsally marginate and laterally denticulate. Sides of the declivous face of the propodeum weakly marginate. Propodeal spiracle round and above mid height in lateral view.

Petiole subrectangular and thick. Anterior border of the petiole straight and anterolaterally strongly carinate. Ventral process of the petiole very large, stout and triangular. Postpetiole in dorsal view with sides gently diverging posteriorly. Postpetiolar sternite anteromedially with a marked subtriangular projection, gently convex posteriorly in side view. Constriction between postpetiole and gaster impressed. Gastral tergite I about 2/5 longer than the postpetiole and convex on the curvature. Remaining gastral tergites and sternites curved ventrally.

Legs not very short. All tibiae with a pectinate spur. Spurs of fore legs without basal spine. Fore basitarsi longer than the mid ones. Hind basitarsi about 1/4 shorter than hind tibiae. Second tarsomere of hind legs shorter than pretarsus. Pretarsal claws simple. Arolia absent.

Sculpture. Head, mesosoma, petiole and postpetiole granulopunctate Sides of the head and pleurae with additional irregular rugosities. Gaster smooth and with minute piligerous punctures. Legs punctate.

Body covered by hairs of three main types: (1) short, dense, suberect or subdecumbent on the whole body, suberect and sparse on the funicular joints; (2) long, erect on the whole body, slightly shorter on the scapes, absent on the funiculi; (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.

Colour. Light brown.

Measurements in mm and Indices: TL 3.20-3.26; HL 0.71-0.72; HW 0.64-0.65; EL 0.03-0.04; SL 0.49-0.50; WL 0.90; PeL 0.23-0.24; PeW 0.32-0.33; HFeL 0.52-0.53; HTiL 0.44-0.45; HBaL 0.33-0.34; LS4 0.38; LT4 0.75-0.77; CI 90.1-90.3; SI 69.0-69.4; IGR 0.49-0.51.

Type Material
Holotype worker labeled: "Thailand, Doi Inthanon, 7.XI.85, Lob1 & Burckhardt", in ; one paratype worker, same data as the holotype in.

Etymology
Siamense is a neologism indicating the provenance from Thailand.