Xenomyrmex

The species of Xenomyrmex form rather small colonies and nest in plant-cavities, such as those of oak-galls, twigs, Acacia thorns, epiphytic Bromeliads (Tillandsias). In the field the various forms are easily mistaken for minute species of Solenopsis, like Solenopsis picta and Monomorium, especially Monomorium floricola and Monomorium ebeninum, which nest in the same situations. From the fact that the types of Xenomyrmex stollii were found in a huge oak gall, which also contained a colony of Camponotus abscisus, Forel concluded that Xenomyrmex was probably a parasitic or symbiotic genus like Formicoxenus, but this opinion has received no support from subsequent observations. The generic name is therefore a misnomer. (Wheeler 1931)

Nomenclature

 *  XENOMYRMEX [Myrmicinae: Formicoxenini]
 * Xenomyrmex Forel, 1885a: 369. Type-species: Xenomyrmex stollii, by monotypy.
 * Xenomyrmex senior synonym of Myrmecinella: Wheeler, W.M. 1931a: 129.
 * MYRMECINELLA [junior synonym of Xenomyrmex]
 * Myrmecinella Wheeler, W.M. 1922d: 1. Type-species: Myrmecinella panamana, by original designation.
 * Myrmecinella junior synonym of Xenomyrmex: Wheeler, W.M. 1931a: 129.

Description
Wheeler 1931:

Worker
Small, monomorphic, with rather thick, smooth or delicately sculptured integument. Head rather large, subrectangular, with feebly rounded sides and slightly concave posterior border. Eyes small, flattened, at the anterior third of the head; ocelli absent. Mandibles triangular, with strongly convex external border, the terminal border provided with three stout apical and a few indistinct basal denticJes. Maxillary palpi 4-jointed; labial palpi 2-jointed. Antennre ll-jointed, the basal funicular joint elongate; joints 2-7 small and transverse, the last three joints forming a club, the last joint swollen and longer than the two basal joints· which are unequal and scarcely longer than broad. Clypeus short and convex, in the middle extending backward between the frontal carinre, and projecting anteriorly as a broad lobe with a concave median border and on each side a stout, somewhat outwardly curved tooth. Frontal carinre short, somewhat diverging posteriorly and rather widely separated. Frontal area and groove obsolete. Thorax slender, much narrower than the head, shaped much as in Monomorium, broadest through the pronotum, with pronounced mesoepinotal constriction; epinotum small, sub cuboidal, unarmed. Petiole small, subcylindrical, non pedunculate, parallel-sided, feebly convex above and below, but without a distinct node, anterodorsally with a tooth or angle on each side. Postpetiole small and short, scarcely broader than the petiole, convex above. Gaster about the size of the head, oval, somewhat flattened dorsoventrally, narrowed anteriorly towards the petiole. Legs with distinctly incrassate femora and stout, clavate tibie; claws simple.

Queen
Much larger than the worker. Head longer and more rectangular. Eyes flattened as in the worker but larger; ocelli small. Frontal area and anterior portion of frontal groove distinct. Thorax elongate-elliptical, as in Monomorium, nearly three times as long as broad, narrower than the head, with elongate mesonotum and small scutellum. Petiole, postpetiole and appendages like those of the worker, gaster much more voluminous, elongate-elliptical. Fore wings with open submarginal and discal cells and a single long cubital cell; hind wings without veins.

Male
As small as the worker. Head rather large, through the eyes somewhat broader than long, convex above, broader behind than in front, with broadly rounded posterior corners and short, straight cheeks. Eyes placed anteriorly, large and convex, nearly half as long as the sides of the head; ocelli small, prominent and widely separated. Clypeus convex, its anterior border narrowly concave in the middle, with a vestigial denticle on each side. Mandibles small and narrow, their truncated terminal border with three or four subequal denticles. Antennae rather long, 12-jointed; scapes cylindrical, as long as the two basal funicular joints together, first funicular joint not enlarged but the second distinctly thicker than the more apical joints; last joint as long as the two preceding joints together. Thorax proportionally shorter than in the female, narrower than the head, with large pro-mesonotum and small epinotum; mesonotum as broad as long, with distinct notauli ("Mayrian furrows"); scutellum and mesosterna large and convex. Petiole above with a rounded, distinct, but low node. Postpetiole and gaster shaped as in the worker. Genitalia somewhat retracted; stipes rounded triangular; volsella: biramous and pecuJiarJy contorted; sagitta: long and slender. Legs not incrassated. Venation of forewings much reduced, only the subcostal and median cells, the base of the radial vein and the pterostigma remaining, or in some cases only the pterostigma and base of the subcostal vein; hind wings veinless as in the female.