Tetramorium mexicanum, Bolton, B., 1979

Bolton, B., 1979, The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Malagasy region and in the New World., Bulletin of the British Museum (Natural History) Entomology 38, pp. 129-181 : 161-162

Tetramorium mexicanum sp. n.

(Figs 52 - 54)

Holotype worker. TL 4.9, HL 1.04, HW 0.92, CI 88, SL 0.88, SI 96, PW 0.74, AL 1.38.

Mandibles longitudinally rugulose. Frontal carinae strongly developed to level of posterior margin of eye but behind this rapidly decreasing and becoming indistinguishable from the remaining cephalic sculpture. Antennal scrobes weak, not capable of accommodating the scapes. Antennal scapes long, SI 96 in holotype, with a range of 94 - 99 in entire type-series (in other members of the complex SI 90 or less). With the head in full-face view the scapes when laid back just exceed the occipital corner. Eyes relatively small, maximum diameter 0.20, about 0.21 x HW. Propodeal spines long, strong and acute; metapleural lobes very elongate-triangular. Outline shape of alitrunk and pedicel as in Fig. 53. Dorsum of head coarsely and irregularly rugose, vermiculate in places, and with numerous cross-meshes, many of which are broken or incomplete. Occiput with a coarse rugoreticulum. Dorsal alitrunk coarsely and sharply rugose, the rugae predominantly longitudinally sinuate or vermiculate but forming a reticulum in places. Petiole and postpetiole similarly but less strongly sculptured. Punctulate ground-sculpture feeble on head and alitrunk dorsally but becoming more distinct on petiole and postpetiole. First gastral tergite unsculptured except for hairpits. Pilosity quite spectacularly developed, with long fine acute hairs abundant on all dorsal surfaces; the longest of those on the pronotum> 1.5 x maximum eye diameter. Leading edge of antennal scapes and dorsal (outer) surfaces of hind tibiae with numerous long hairs, the longest of which distinctly exceed the maximum diameter of the appendage from which they arise. Colour red-brown.

Paratype workers. TL 4.8 - 5.2, HL 1.00 - 1.12, HW 0.90 - 100, CI 87 - 90, SL 0.88 - 0.98, SI 94 - 99, PW 0.74 - 0.80, AL 1.36 - 1.48 (14 measured). As holotype but some lighter in colour, reddish orange, and with the metapleural lobes broader than in the holotype. Metanotal groove variously developed. In holotype visible in profile but in most paratypes not at all impressed. Eyes uniformly small, maximum diameter 0.19 - 0.21, about 0.20 - 0.22 x HW. Cephalic sculpture rather more sharply developed in Tepic paratypes than in those from Puerto Los Mazos.

Holotype worker, Mexico: lalisco, Puerto Los Mazos, 10 miles SW. Autlan, 4400 ft, 25. ix. 1973, leaf litter forest floor (A. Newton) (MCZ, Cambridge).

Paratypes. Mexico: 2 workers with same data as holotype; 12 workers, Nayarit, Tepic (W. M. Mann) (MCZ, Cambridge; BMNH; LACM, Los Angeles; USNM, Washington).

This large species is characterized by its long antennal scapes, very long dense pilosity, coarse sculpture and small eyes. The first two characters are absolutely diagnostic in available material, the length of the hairs not being approached by any sample of any other species of the complex, and the SI range of 94 - 99 is higher than in all others, whose combined SI range is 76 - 90.