Proceratium transitionis

Identification
A Proceratium species appearing as basalmost of the micrommatum clade and differing from all the other species of this clade, by the worker clypeus broad and subrectangular instead of narrow, triangular or convex and by the petiole 1/4 longer than broad instead of at most 1/5 longer than broad; and from the next in-group species, Proceratium lattkei, in the worker, by the propodeal dorsum with tumulus; and from all the other species of the micrommatum clade except lattkei, by the worker mid legs with a spur and by the broad, diverging frontal carinae. (Baroni Urbani and de Andrade 2003)

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

Nomenclature

 *  transitionis. Proceratium transitionis De Andrade, in Baroni Urbani & De Andrade, 2003b: 119, figs. 56, 57 (w.) COLOMBIA.

Proceratium transitionis is noteworthy, appearing in our analysis as the basalmost species of the micrommatum clade. It resembles nonetheless the species of the stictum clade by sharing with them the broad clypeus. Within the micrommatum clade, it shares with all the members of the goliath group the broad, diverging frontal carinae and the dense and long pilosity. transitionis shares, however, with its next in-group species Proceratium lattkei and with all the other species of the genus Proceratium the mid tibiae with spur, a character absent in all the other species of the micrommatum clade. Of course transitionis differs from all the species of the stictum clade by missing the spine on the spur of the fore legs and by the palp formula 3,2 instead of 4,3.

Worker
Head longer than broad and with the sides gently diverging posteriorly. Vertex in full face view slightly convex. Clypeus broad, subrectangular protruding anteriorly and narrowly surrounding the antennal insertion. Antenna1 socket with broad torulus. Frontal carinae broad, separate from each other, covering part of the antennal insertions. Floor of the frontal carinae with a central sulcus. Frontal area behind the frontal carinae gently convex. Lateral expansions of the frontal carinae relatively broad, slightly raised, stro~lgly diverging on the two anterior thirds and parallel, low and marginate on the posterior third. Genal carinae marked, prolonging towards the hypostomal bridge and bounding a weakly concave gular area. A sulcus is present between the genal carinae and the gular area. Eyes present, composed by a convex facet placed below the midline of the head. Scapes thicker in their distal half and much shorter than the vertexal margin. First funicular joint slightly longer than broad. Funicular joints 2-10 broader than long. Last funicular joint as long as the sum of joints 6-10. Mandibles (only left visible) with 2 large teeth before the apical tooth. Palp formula 3,2.

Mesosoma slightly convex in profile. Promesonotal and propodeal sutures absent. Promesopleural and mcsometapleural sutures impressed on the ventral hall only. Basal face of the propodeum weakly convex and with a shining medial tumulus. Area behind the propodeal tumulus with a transversal, superficial impression. Sides between the propodeal basal and declivous faces unarmed. Declivous face of the propodeum with the posterior sides marginate. Ventral part of the propodeal lobes obtuse, dorsal part round and slightly crenulate.

Petiole 1/4 longer than broad, in dorsal view diverging in the anterior third and convex posteriorly. Anterior border of the petiole superficially carinate and medially concave. Ventral process of the petiole needle- shaped. Postpetiole slightly less than 1/2 of the length of the gastral tergite I (LT4), in dorsal view with convex sides. Posterior half of the postpetiolar dorsum weakly convex in the middle. Postpetiolar sternite anteromedially with a marked subround border. Posterior half of the postpetiolar sternite gently convex. Constriction between postpetiole and gastral segment I deeply impressed. Gastral tergite I markedly round. Gastral sternite I (LS4) very short medially. Sides of gastral sternite I without carina. Remaining gastral tergites and sternites curved ventrally.

Legs slightly elongate. Mid tibiae with spur. Spurs of fore legs without a basal spine. Fore basitarsi longer than the inid ones. Hind basitarsi about 1/7 shorter than hind tibiae. Second tarsomere of mid and hind legs longer than each the third and fourth tarsomeres, and shorter than pretarsus. Pretarsal claws simple. Arolia very small.

Sculpture. Head granulate, sparsely and irregularly rugulose, the granulation larger posteriorly. Mesosoma, petiole and postpetiole irregularly granulate-foveolate, the foveae more superficial on the mesonoturn, some granules raised as small peaks. Mesonotum, lower meso- and metapleurae with additional irregular rugosities. First gastral tergite granulate, the granulation denser on its sides and posteriorly. Legs and antennae superficially granulate-punctate.

Body covered by hairs of three main types: (1) short, dense, subdecumbent on the whole body, sparse and erect on the funicular joints; (2) long, suberect and relatively dense on the whole body, absent from the antennae; (3) shorter than hair type (I), dense, subdecumbent and appressed on the funicular joints only. In addition the funicular joints bear whitish, thick, appressed, short, sparse hairs, and the scapes with hairs similar to type (2) but shorter.

Colour dark fessugineous-brown with slightly lighter legs.

Measurements in mm and Indices: TL 5.00; HL 1.20; HW 1.04; EL 0.08; SL 0.72; WL 1.40; PeL 0.56; PeW 0.42; HFeL 1.04; HTiL 0.85; HBaL 0.64; LS4 0.20; LT4 1.16; CI 86.7; SI 60.0; IGR 0.17.

Type Material
Holotype worker from Colombia labelled "Santander Virolin, Costllla de Fara, 6°6'19"N 73°13’2o” W, 1800 m, 29.III.1999, 1 worker (holotypc), E. L. Gonzales" in.

Etymology
From the Latin transitio (Cicero), referred to the characters that this species shares with the stictum clade.