Pseudomyrmex opaciceps

P. opaciceps is evidently a generalist twig-nesting Pseudomyrmex, but Janzen also collected it from an Acacia cornigera tree overgrown by vines and unoccupied by the P. ferrugineus group (5 mi. W Retalhuleu, Guatemala, collection numbers M010714966-A and M010716966-D). (Ward 1993)

Identification
Ward (1993) - This species is distinguished from the closely related and sympatric Pseudomyrmex gracilis by a modest but consistent difference in head sculpture. In workers and queens of P. opaciceps the punctulate-coriarious sculpture and associated dense pubescence obscure the sheen of the head, producing a matte appearance under soft light, while in P. gracilis the head remains at least weakly shining. In addition the workers and queens of P. opaciceps average smaller in size than those of P. gracilis and they have a more slender petiole (PLI < 0.48). Finally, P. opaciceps has a distinctive and largely invariant color pattern: the pale yellow or orange-brown petiole, postpetiole and gaster contrast with the much darker head and mesosoma. This is not observed in Central American P. gracilis, although a similar color pattern occurs in some Colombian populations of P. gracilis, and it also seen in some individuals of the more distantly related South American species Pseudomyrmex venustus (F. Smith).

Distribution
Guatemala, Mexico and El Salvador.

This taxon was described from Guatemala.

Nomenclature

 *  opaciceps. Pseudomyrmex opaciceps Ward, 1993: 159, fig. 5 (w.q.m.) GUATEMALA.

Description
measurements (n=14). —HL 1.30-1.42, HW 1.33- l .43, MFC 0.040-0.058, CI 0.99-1.04, REL 0.57-0.61, REL2 0.56-0.61, OOI 0.14-0.68, VI 0.65-0.71, FCI 0.029-0.042, SI 0.46-0.50, SI2 0.77-0.88, PI 0.36-0.39, PDI 1.12-1.37, MPI 0.059-0.076, NI 0.65-0.70, PLI 0.42-0.47, PWI 0.38-0.43, PPWI 0.92-1.16.

With the traits of the P. gracilis group and the following more specific features. Head about as broad as long; anterior margin of median clypeal lobe straight to weakly convex; pronotum with blunt dorsolateral margination; mesonotum more steeply inclined than basal face of propodeum; petiole long and slender (see PLI and PWI values) with a distinct anterior peduncle; head densely punctulate-coriarious and matte; standing pilosity abundant, pale silvery-white, not black. Color: head and mesosoma dark brown to black, mandibles and appendages lighter brown; petiole, postpetiole and gaster a contrasting pale luteous brown or orange-brown. Portions of the fronto-clypeal complex, malar area, and mandibles may also be luteous brown.

Type Material
Holotype worker. —GUATEMALA Retalhuleu: Puente Samala, 3.8 mi. NE San Felipe, 24.vii.1966, D. H. Janzen W006724966. HW 1.43, HL 1.42, EL 0.85, PL 0.89, PH 0.39.

Paratypes. —Series of 11 workers with same data as holotype; large series of ca. 60 workers and 10 males with the same locality and collector as holotype but the following dates and collection numbers: 18.vii.1966 M002718966 (possibly mis-labelled — see below), 18.vii.1966 W002718966, 18.vii.1966 W004718966, 18.vii.1966 W005718966 (possibly mis-labelled — see below), 23.vii.1966 W002723966, 24.vii.1966 W001724966, 24.vii.1966 W003724966 (, LACM,, , , , ).