Colobostruma biconcava

This is a rare species found in the ACT and South Australia. Nothing is known of its biology.

Identification
Shattuck (2000) - C. biconcava can be separated from other species in the alinodis-group by the presence of a 4-segmented antenna with a relatively short second funicular segment. It is most similar to Colobostruma biconvexa but differs in having the posterior faces of the petiole and postpetiole weakly concave, whereas these faces are convex in biconvexa. Additionally, biconcava is known from the Australian Capital Territory and South Australia while biconvexa is known only from Queensland.

Distribution
Known from the Australian Capital Territory and South Australia.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  biconcava. Colobostruma biconcava Shattuck, in Bolton, 2000: 35 (w.) AUSTRALIA.

Worker
HOLOTYPE WORKER. TL 2.3, HL 0.55, HW 0.49, CI 89, ML 0.11, MI 20, SL 0.25, SI 51, PW 0.33, AL 0.60. Anterior region of head rounding gradually from the dorsal to lateral surfaces, not phragmotic. In full-face view ridge immediately in front of eye weakly concave. Frontal lobes and lateral margins of clypeus smooth and relative to the surrounding surface of the head. Mandibles broadly triangular. Hairs absent from the dorsum of head. Posterior margin of head uniformly concave. Antenna with 4 distinct segments, sometimes with the second funicular segment apparently partially subdivided distally (this partial segment always much shorter than the second segment); the second segment approximately one-third longer than the first segment. Scape elbowed and without a subbasal lobe. In dorsal view the widest point of the pronotum is at the humeral angles. Propodeum high, its posterior face greater in height than the petiolar node and with broad, thin lamellae; in profile the dorsum of the alitrunk gently and weakly arched. Lateral postpetiole drawn outwards into a thin flange-like wings, the wings with translucent windows along both their anterior and posterior margins, the windows separated by a narrow band of thickened integument and the anterior windows always smaller than the posterior windows. Posterior faces of petiole and postpetiole concave, the concavity of the postpetiole low, immediately above the gastral surface. First gastral tergite superimposed with weakly defined reticulate sculpturing, its anterior one-quarter with a series of low longitudinal carinae. Body colour honey yellow, dorsum of head slightly darker, antennae and legs slightly lighter, gaster with an incomplete, weakly infuscated medial band.