Proceratium mexicanum

The types were collected from the litter of a palm thorn forest.

Identification
A member of the micrommatum clade. Resembling Proceratium convexiceps, but differing from it in the worker, by the following characters: area between basal and declivous faces of the propodeum with a clear transversal carina (absent or poorly marked only laterally in Proceratium micrommatum), and body sculpture more superficial than in micrommatum. (Baroni Urbani and de Andrade 2003)

Within the United States, this species can be separated from others by the low, rounded petiole, and lack the median protrusion of the clypeus found in other species (Proceratium pergandei, Proceratium compitale, Proceratium chickasaw, Proceratium creek) with a low petiole; it also lacks a pectinate spur on the middle tibia (Baroni Urbani and de Andrade 2003).

Distribution
The northern limit of this species is extreme southern Texas, United States.

Distribution based on Regional Taxon Lists
Neotropical Region: Guatemala, Mexico.

Nomenclature

 *  mexicanum. Proceratium mexicanum De Andrade, in Baroni Urbani & De Andrade, 2003b: 155, figs. 71-73 (w.q.m.) MEXICO.

Taxonomic Notes
The male Proceratium micrommatum reported from Hidalgo County, Texas by Ward (1988) is probably this species. Other specimens of are known from nearby sites in Mexico.

Two workers from Oaxaca (Valle Nacional) differ from the other workers by the stouter body (TL 3.75 mm), by the basal face of the propodeum more convex, by the propodeal carina ticker and by the massive petiole (PeL 0.40 mm, Pew 0.40-0.41 mm).

Two workers from Mesa de Chipinque are very large (TL 3.80-4.00 mm) and have the petiole (PeL 0.38-0.39 mm, PeW 0.39 mm) similar to the workers from Valle Nacional.

A worker from Ocosingo has the hairs slightly longer than the other specimens.

A gyne from El Bonito differs from the other gynes by the hairs longer, resembling the hairs of the worker from Ocosingo.

Ward, 1988 attributed a male from south Texas (Hidalgo County) to Proceratium micrommatum or to the micrommatum complex. We added that this male is relatively small (HW 0.66 mm), with strongly recurved gaster (IGR 0.32) and mid tibiae without spur. We examined Proceratium mexicanum workers from Monterrey (ca. 220 km from the locality of the Texan male studied by Ward). The male from El Bonito (San Luis Potosi) here tentatively attributed to mexicanum differs from Ward's male in the following: HW 0.61 mm instead of 0.66 mm, IGR 0.32 instead of 0.37. We did not see the specimen in question but it might belong to mexicanum.

If our interpretation of mexicanum is correct, a certain amount of geographic variability should characterize this species. We can not exclude, however, that the collection of additional material might allow the separation of one or more species from it.

Worker
Head longer than broad, slightly narrower anteriorly than posteriorly. Vertex in full face view weakly convex medially. Clypeus medially reduced, triangular or subround, recognizable between and longer than the antennal sockets. Antenna1 socket with broad torulus. Frontal carinae close to each other, not covering the antennal insertions. Frontal area behind the frontal carinae weakly convex. Lateral expansions of the frontal carinae relatively narrow, raised and gently diverging posteriorly. Genal carinae present and well marked. A superficial sulcus between the genal carinae and the gular area. Eyes composed by a small convex facet below the midline of the head. Scapes thicker in the distal half and far short of the vertexal margin. First funicular joint 1/3 longer than broad. Funicular joints 2-10 broader than long. Last funicular joint as long as the sum of joints 6-10. Mandibles with 3 denticles before the apical tooth. Palp formula 3,2.

Mesosoma gently convex in side view. Promesonotal and propodeal sutures absent. Promesopleural and mesometapleural sutures impressed on the ventral half only. Basal face of the propodeum gently convex or declivous posteriorly and with traces of a superficial, transverse sulcus close to the declivous face; the sulcus postero-laterally strongly carinate; in some specimens the carina transformed in a tooth on each side between the basal and declivous face. Declivous face of the propodeum with the sides superficially marginate, the margin variably crenulate. Propodeal lobes subround or truncate and with variably crenulate margin. Propodeal spiracles small and tumuliform.

Petiole slightly longer than or as long as broad. Petiole in dorsal view with the sides subparallel in the anterior fourth and convex posteriorly. Anterior border of the petiole straight or gently concave and carinate. Ventral process of the petiole subtriangular and small. Postpetiole slightly less than 1/2 of the length of the gastral tergite I (LT4). Postpetiole in dorsal view anterolaterally subround and with the sides convex. Postpetiolar dorsum with a swelling close to the posterior border. Postpetiolar sternite anteromedially with a marked subtriangular projection. Posterior half of the postpetiolar sternite straight or slightly convex. Constriction between postpetiole and gastral segment I deeply impressed. Gastral tergite I strongly convex on the curvature. Gastral sternite I very short medially. Sides of gastral sternite I variably protruding anteriorly, obtuse or round. Remaining gastral tergites and sternites curved ventrally.

Legs slightly elongate. Mid tibiae without spur. Spurs of fore legs without a basal spine. Fore basitarsi longer than the mid ones. Hind basitarsi about 1/4 shorter than hind tibiae. Second tarsomere of mid and hind legs longer than third and fourth tarsomeres, and slightly shorter than pretarsus. Fourth tarsomere of fore legs much longer than tarsomeres 1-3 and shorter than the sum of tarsomeres 1-2. Pretarsal claws simple. Arolia small.

Sculpture. Head, mesosoma, petiole and postpetiole reticulate-punctate and granulate, the granules very sparse on the head and mesosoma, denser and larger on the petiole and postpetiole. Mesosoma, petiole and postpetiole with additional irregular foveae, the foveae superficial, rare and small on the mesosoma, deeper and more numerous on the petiole and postpetiole. First gastral tergite smooth and with minute, sparse piligerous punctures, the punctures denser, larger and mixed with reticulation on its sides and on the posterior border. Legs and antennae superficially granulate-punctate.

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

Colour dark ferrugineous or dark brown with lighter antennae and legs.

Measurements in mm and Indices: TL 2.93-4.00; HL 0.71-0.91; HW 0.64-0.8 1 ; EL 0.05-0.06; SL 0.45-0.59; WL 0.8 1-1.10; PeL 0.3 1-0.40; PeW 0.27-0.41 ; HFeL 0.55-0.73; HTiL 0.43-0.60; HBaL 0.33-0.50; LS4 0.13-0.1 9; LT4 0.66-0.98; CI 89.0-92.9; SI 62.5-64.8; IGR 0.19-0.21.

Queen
Differing from the worker in the following details: eyes large, about 1/4 of the head length and with ocular pilosity. Ocelli well developed. Funicular joints more elongate.

Mesosoma robust and convex in side view. Parapsidal furrows superficially marked. Scutellum with the sides converging posteriorly and with the posterior border rounded or subtruncate. Metanotum without tooth or spinelike projection. Basal face of the propodeum short, laterally variably carinate and angulate, medially incised and as flat as the declivous face. Petiole about as broad as long.

Sculpture. Granules and foveae rarer and smaller on the mesosoma and on the postpetiole.

Measurements in mm and Indices: TL 3.76-3.90; HL 0.80-0.83; HW 0.73-0.77; EL 0.20; SL 0.54-0.58; WL 1.08-1.16; PeL 0.33-0.35; PeW 0.32-0.35; HFeL 0.68-0.70; HTiL 0.54-0.55; HBaL 0.44-0.47; LS4 0.17-0.18; LT4 0.92-0.94; CI 89.0-92.0; SI 68.3-70.0; IGR 0.18-0.19.

Male
(tentative attribution). Head longer than broad. Vertex in full face view convex. Vertexal margin weakly carinate. Clypeus medially extremely reduced, subround, between and about as long as the antennal socket. Antenna1 socket with broad torulus. Frontal carinae thin, low and diverging posteriorly. Anterior half of the frontal area gently convex and with a variably impressed longitudinal carina, the second half concave. Ocelli large. Compound eyes slightly less than half of the head length, placed largely on the anterior head sides and with ocular pilosity. Scapes reaching the anterior ocellus. First funicular joint broader than the second joint and slightly broader than half of its length. Funicular joints 1-9 about one half longer than broad; joints 10-12 absent. Mandibles elongate, edentate and only with a pointed apical tooth. Palp formula apparently 3,2.

Mesosoma robust. Pronotum perpendicular to the mesonotum. Mesonotum gently convex. Parapsidal furrows marked. Scutellum as high as the mesonotum and in full dorsal view with the posterior border round. Propodeum with distinct basal and declivous faces. Basal face of the propodeum in dorsal view flat, medially sulcate and laterally subangulate. Declivous face of the propodeum perpendicular to the basal face. Metanotuin without median spine-like projection. Propodeal lobes small and subround. Propodeal spiracles small and weakly oriented downwards.

Petiole in profile declivous on the anterior half and strongly convex on the posterior half. Petiole in dorsal view with diverging sides in the anterior third and strongly convex in the two posterior thirds. Anterior border of the petiole concave and carinate. Subpetiolar process in shape of a subtriangular, longitudinal lamella. Postpetiole in side view convex. Postpetiole anteriorly broader than the petiole; postpetiolar sides convex. Anterior border of the postpetiolar sternite with a projecting triangular "lip". Gastral tergite I round. Gastral sternite I broad in the middle. Remaining gastral tergites and sternites curved ventrally.

Legs less elongate than in convexiceps. Hind basitarsi shorter than hind tibiae.

Sculpture. Head, pronotum, mesonotum, scutellum, mesopleurae, petiole, postpetiole, gaster and legs with small piligerous foveae, the foveae more impressed on the two anterior thirds of the cephalic capsule. In addition the petiole and the postpetiole with very sparse, minute granulation. Propleurae sculptured as the pronotum but with few, very thin, rugosities. Propodeum with dense, irregular impressions or small foveae. Metapleurae with thick, irregular rugosities.

Body covered by hairs of three main types: (1) short, dense, subdecumbent on the whole body, suberect and sparser on the funicular joints; (2) long, suberect and sparse on the whole body, slightly longer on the petiole, postpetiole and gaster, absent from the antennae; (3) shorter than hair type (1), dense, decumbent 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 (1) but longer.

Colour. Light brown.

Measurements in mm and Indices: TL 3.57; HL 0.67; HW 0.61; EL 0.28; SL 0.48; WL 1.16; PeL 0.36; PeW 0.31; HFeL 0.82; HTiL 0.65; HBaL 0.57; LS4 0.29; LT4 0.78; CI 91.0; SI 71.6; IGR 0.37.

Type Material
Holotype worker from Mexico labelled "Mex.: Tamps.; Antiguo Morelos 9.VII.1969, S. & J. Peck, Ber 167, palm-thorn for. litter"; 4 paratype workers, same data as the holotype, holotype in, paratypes in MCZ and.

Etymology
"Mexicanum" is a neologism indicating the provenance of the species from Mexico.

References based on Global Ant Biodiversity Informatics

 * Baroni Urbani C., and M.L de Andrade. 2003. The ant genus Proceratium in the extant and fossil record (Hymenoptera: Formicidae). Museo Regionale di Scienze Naturali, Monografie 36: 1-480.
 * Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
 * Del Toro, I., M. Vázquez, W.P. Mackay, P. Rojas and R. Zapata-Mata. Hormigas (Hymenoptera: Formicidae) de Tabasco: explorando la diversidad de la mirmecofauna en las selvas tropicales de baja altitud. Dugesiana 16(1):1-14.
 * Longino J. et al. ADMAC project. Accessed on March 24th 2017 at https://sites.google.com/site/admacsite/
 * Scott-Santos, C.P., F.A. Esteves, C.R.F. Brandao. 2008. Catalogue of "Poneromorph" ant type specimens (Hymenoptera, Formicidae) deposited in the Museu de Zoologia da Universidade de Sao Paulo, Brazil. Papeis Avulsos de Zoologia 48(11):75-88.
 * Vasquez-Bolanos M. 2011. Checklist of the ants (Hymenoptera: Formicidae) from Mexico. Dugesiana 18(1): 95-133.
 * Vásquez-Bolaños M. 2011. Lista de especies de hormigas (Hymenoptera: Formicidae) para México. Dugesiana 18: 95-133