Octostruma trithrix Longino, sp. nov.

(Figs 1E, 3D, 5A, 8A, 40, 42)

Type material. Holotype worker: MEXICO, Chiapas: 8 km SE Salto de Agua, 17.51611, -92.30168, ± 50 m, 100 m, 14 Jun 2008, 2° wet forest, ex sifted leaf litter (LLAMA, Wa-A-08-2-03) [CAS, CASENT0639179]. Paratype workers, queen: same data [UCDC, CASENT0639180; UVGC, CASENT0639181; EAPZ, CASENT0639182; CAS, CASENT0639183; JTLC, CASENT0639184]; same data except 17.51442, -92.29500, ± 50 m, 70 m (LLAMA, Wa-A-08-1-05) [ECOSCE, CASENT0639174; USNM, CASENT0639175; MCZC, CASENT0639176; MZSP, CASENT0639177; CAS, CASENT0639178].

Geographic range. Northern Mexico (Nuevo León) to Honduras.

Diagnosis. Mandible with 8 teeth (Fig. 3D), tooth 1 a broad blunt lamella, strongly differentiated from tooth 2, teeth

2-5 acute, similar in shape, with denticles between them; teeth 5-8 forming an apical fork, with 5 and 8 large, 6 and 7 small partially confluent denticles (O. balzani complex); face setation as in Fig. 5A, erect setae present on posterolateral margins of head (absent in O. amrishi and O. gymnogon); in most workers of a series, a seta present between anterior seta on side of head near eye and medial vertex seta (this seta typically absent in O. balzani, O. megabalzani, O. amrishi, and O. gymnogon); mesosomal dorsum with one pair of erect setae (absent in O. amrishi, O. gymnogon; 2 pairs in O. lutzi); metanotal groove not impressed in profile view (impressed in O. balzani and O. megabalzani).

Description. Worker. HW 0.54-0.62, HL 0.50-0.58, WL 0.52-0.66, CI 102-112 (n=7). Matching in almost every respect the description for O. balzani, except the differences outlined in the Diagnosis and key. In addition to characters in the Diagnosis, first gastral tergite typically with 8-16 erect setae, color red brown.

Queen. HW 0.59-0.64, HL 0.55-0.60, WL 0.70-0.75, CI 103-107 (n=7). Similar to O. balzani in most respects; 4-6 setae across vertex between compound eyes (2-4 in O. balzani); postpetiolar disc with 4-6 erect setae (2-4 in O. balzani).

Biology. In the southern portion of its range, Octostruma trithrix occurs in a variety of forested habitats: wet to seasonal dry, second growth to mature. It is typically lowland, occurring from sea level to around 700 m. In the northern part of the range it occurs in cloud forest, up to 1200 m elevation. Almost all collections are from Berlese and Winkler samples of sifted litter and rotten wood from the forest floor. In quantitative 1 m 2 litter plot samples, within-sample abundance is tens of workers or fewer, but the species can occur frequently, suggesting a high density of small colonies. Dealate queens may occur together with workers in litter samples.

Comments. See under O. balzani.

Etymology. The name refers to anterior row of three spatulate setae on the face. It is a noun in apposition and thus invariant.