1903.] NATURAL SCIENCES OF PHILADELPHIA. 221 



ants of these two genera differs very decidedly. The following are 

 the leading diagnostic characters of the genus Leptothorax. 



LEPTOTHORAX Mayr. 



Worker. — Small, monomorphic. Head longer than broad, and 

 broader than the thorax, ^landibles broad, 4-5-toothed. Maxillary 

 palpi 5-jointed; labial palpi 3-jointed. Clypeus variable in shape, 

 slightly convex or impressed in the middle, its anterior border some- 

 what rounded, entire or sinuately excised in the middle. Frontal 

 carinse almost straight, diverging very little behind. Antennse 11- 

 or 12-jointed, usually with a distinctly 3-jointed club. Frontal area 

 present. Eyes of moderate size, near the middle of the lateral surface 

 of the head. Ocelli occasionally present, especially in ergatoid or 

 subergatoid individuals. Thorax slender, usualh^ somewhat broader 

 in front, at least above, and narrower behind. Promesonotal suture 

 obsolete; mesoepinotal suture present or absent, the thorax at this 

 region either without any constriction, with a faint or a very decided 

 (subgen. Dichothorax) constriction. Epinotum armed with a pair of 

 teeth, or spines of variable development. Petiole with a short pedun- 

 cle in front and surmounted by a node of variable form, its lower an- 

 terior surface armed with a median tooth. Postpetiole nodiform, 

 sometimes more campanulate, unarmed below. Gaster large, broadly 

 elliptical, compressed dorsoventrally, its basal three-fourths formed 

 by the first segment. Sting well developed, at least in many of the 

 species. Legs rather stout, the femora fusiform, somewhat incrassated 

 in the middle, the tibiae tMcker toward their distal ends. Spurs of 

 middle and hind legs simple, not pectinate. Integument very hard. 

 In most species the hairs on the body, and in a few also those on the 

 appendages, are short, erect, clavate and under a high magnification 

 finely crenulate. Our species are yellow, brown, red or black, and the 

 majority of them have the head, thorax and pedicel more or less sculp- 

 tured and in great part opaque. The gaster in all our species is very 

 smooth and shining. 



Female. — Somewhat larger and more robust than the worker, or of 

 the same size. Antennse of the same number of joints. Eyes and ocelli 

 moderately prominent. Thorax with its sides subparallel or somewhat 

 bulging in the middle. Mesonotum conspicuously flattened. Epi- 

 notal spines shorter and often stouter than in the worker. Basal 

 surface of epinotum nearly horizontal. Petiole and postpetiole like 

 the corresponding segments of the worker, the node of the former often 

 more acute. Gaster like that of the worker, at least its basal two- 



