1912] Wheeler — Ants of the Genus Myrmecocystiis Wesmael 177 



lateral and posterior borders. Eyes very convex, fully half as long as the cheeks. 

 Ocelli minute. Mandibles 7- toothed, with the apical tooth longest and curved. 

 Clj'peus convex but not carinate in the middle, flattened and depressed on the 

 sides. Frontal area distinct. Antennse moderately slender, scapes extending 

 about 2/5 their length beyond the posterior border of the head. Thorax much 

 as in the other species of the genus; pronotum as broad as long; mesoepinotal 

 constriction shallow; epinotum with subequal base and declivity, bluntly angular. 

 Petiole half as broad as the epinotum, cuneate in profile, inclined forward, com- 

 pressed anteroposteriorly, with flattened posterior and feebly convex anterior 

 surface and blimt border, which, seen from behind, is straight and entire. Gaster 

 and legs of the usual conformation. 



Mandibles subopaque, densely and finely striated. Clypeus and head very 

 smooth and shining. Thorax and gaster more opaque, especially on the dorsal 

 surface, finely shagreened. 



Hairs and pubescence white, the former short, erect, absent or very sparse on 

 the scapes, moderately abundant on the head, somewhat sparser on the thorax and 

 gaster, short, sparse and reclinate on the tibiae. Pubescence short and delicate, 

 moderately abundant on the head, thorax, gaster and appendages. 



Dark brown; anterior half of head, antennse, palpi and legs paler; mandibles, 

 anterior border of clypeus and cheeks, tibiae and tarsi yellowish or pale brown. 

 Mandibular teeth black. 



Described from numerous workers taken from several colonies 

 at Yuma, Arizona. 



This species differs from lugubris in the shape of the head and 

 petiole, from the various forms of melliger in its much smaller 

 size and in the inclination and shape of its petiole. 



M. yiima inhabits small crater nests, 3-4 inches in diameter, 

 in the pebbly desert. The nest entrance is small, often less than 

 ^ in. in diameter and often surrounded by small twigs and 

 dead leaves. The numerous remains of small insects, frequently 

 seen around the edges of the craters, show that this ant is pred- 

 atory in its habits. The colonies are quite populous so that they 

 cannot be regarded as incipient colonies of any of the subspecies 

 or varieties of AI. melliger. At first sight M. yuma may be readily 

 mistaken for the small desert form of Dorymyrmex pyramicus 

 Roger var. niger Pergande. 



M. jruma var. fiaviceps var. nov. 



Worker. Length 2.5-3.5 mm. 



Dififering from the typical form in color and pubescence and in having the head 

 more rectangular and broader in front. The brown coloration of the body ajid 

 appendages is paler and the yellow color on the head extends back over the gula 



