SYSTEMATIC POSITION. 29 
Brown; thorax, scapes and legs somewhat paler; mandibles yellowish; apices of 
the individual funicular joints blackish. 
Female (dealated): Length 4.5-5 mm. 
Head, without the mandibles, but little longer than broad, with rather angular pos- 
terior corners, straight, subparallel sides and straight posterior border. Eyes large and 
rather convex. Mandibles and clypeus like that of the worker, scapes proportionally 
shorter and stouter. Thorax large, as broad as the head, elongate elliptical, nearly 
three times as long as broad. In profile the scutellum is very convex, projecting 
above the meso- and epinotum. Epinotum with very short base and long abrupt 
declivity. Petiolar node erect, more than half as broad as the epinotum. Gaster 
elliptical, somewhat shorter and a little broader than the thorax. Legs slender. 
Sculpture like that of the worker but more opaque; mandibles and clypeus also 
less shining. 
Scattered hairs more numerous than in the worker and also present in small numbers 
on the vertex, gula, mesonotum, prosternum, and fore coxae. There is also a row of 
short hairs along the posterior margin of each gastric segment. Pubescence dis- 
tinctly longer, more silky, and denser than in the worker. 
Dark brown; antennae, legs and posterior margins of the gastric segments reddish; 
mandibles, sutures of thorax and articulations of legs yellow. 
Male: Length 2.8-3 mm. 
Head much flattened; including the flattened eyes, as broad as long. Vertex and 
ocelli prominent. Cheeks short. Mandibles small, overlapping, with a single, acu- 
minate apical tooth. Anterior clypeal border straight. Antennae slender; scape 
only between three and four times as long as broad; first funicular joint globose, 
broader than any of the other joints; second joint much longer than the ncape; joints 
3-5 growing successively shorter; joints 6-12 considerably shorter and more slender. 
Thorax very robust, elliptical, broader than the head, which is over-arched by the 
protruding, rounded mesonotum. Scutellum even more prominent than in the female. 
Epinotum with subequal base and declivity, the former slightly convex, the latter 
feebly concave, forming an angle with each other. Petiole small, its node with rather 
blunt margin, slightly inclined forward. Gaster very small, elongate elliptical, with 
small rounded external genital valves. Legs slender. Wings with a four-sided discal 
cell and two well developed cubital cells. The costal margin is depressed or folded 
in just proximally to the stigma. 
Sculpture, pilosity and pubescence as in the worker; color more like that of the 
female, except that the antennae, legs, mandibles and internal genitalia are pale, 
sordid yellow. Wings smoky hyaline, with brown veins and stigma. 
I. humilis belongs to a small group of neotropical species embracing also 1". iniquus 
Mayr, dispertitus Forel, Jceiteli Forel and melleus Wheeler. The workers of Jceiteli and 
melleus may be at once distinguished by their color, the former having a yellowish 
brown head and thorax and the remaining parts brownish yellow; the latter being 
pale yellow with a blackish gaster and funiculus. In these and in I. iniquus and 
dispertitus the mesoepinotal constriction is much deeper than in humilis and the meso- 
and epinotum are of a different shape. The mesonotum in profile does not form a 
continuous, even line with the pronotum and the epinotum is very protuberant and 
almost conical. I. humilis represents a transition from the above group of species 
to that of I. analis Ern. Andre, which is very common in the Southern States. This 
species has a shorter, more robust thorax, more like that of Tapinoma, and much less 
constricted in the mesoepinotal region. 
The above description was drawn from a number of workers, males and females 
taken from the same nest in Baton Rouge, La., by Mr. Wilmon Newell. The types 
described by Mayr were captured by Prof. P. de Strobel in the environs of Buenos 
Aires. 
