I92 WILLIAM MORTON WHEELER. 



chsetae, and hairs like those on the clypeus and mandibles for 

 brushing the fore tarsi, must be of considerable utility. Ants 

 living in sandy deserts often have the gular hairs unusually long, 

 and well developed, probably because sand particles, with their 

 sharp edges, are more injurious to the delicate combs of the 

 strigil and metatarsus and interfere more with their normal move- 

 ments of occlusion than do particles of soil. If, as I believe, the 

 circumoral macrochaetae have the function here assigned to them, 

 they may be designated as ammochcetce to distinguish them from 

 the long hairs or bristles on other portions of the ant's body. 



The absence of ammochaetae in several desert ants, such as the 

 species of Monomorium and Pheidole, is probably to be explained 

 by the very small size of the workers in both of these genera, and 

 the fact that the soldiers of Pheidole do not excavate and rarely 

 leave the galleries of the nest. For the same reason the ammo- 

 chaetae are usually absent or feebly developed in the males of 

 xerophilous species. That the workers and females of several 

 other desert ants belonging to the genera Solenopsis, Cremastogas- 

 ter, Camponohis, etc., should lack these structures is no more 

 surprising than that many desert plants have failed to acquire 

 the peculiar adaptive characters of the Cactaceae. We may now 

 consider briefly the occurrence of the ammochaetae in the various 

 genera of xerophilous ants. 



Subfamily Myrmicin/e. 

 Pogonomyrmex Mayr. — This genus embraces a number of 

 species peculiar to North and South America and assignable to 

 three subgenera, Janetia Forel, Ephebomyrmex Wheeler and 

 Pogonomyrmex s. str. The single known species of Janetia (J. 

 mayri Forel) occurs in Colombia. Ephebomyrmex comprises 

 some four species, E. ndgelii Forel of Brazil, schmiiti Forel of 

 Haiti, imberbicidns Wheeler of Texas and townsendi sp. no v. of 

 Chihuahua. None of. the species of these two subgenera has 

 ammochaetae, and it should be noted that J. mayri and the first 

 two species of Ephebomyrmex occur in comparatively humid 

 regions, and that E. imberbiculus and townsendi though xerophi- 

 ious, are not true desert ants. Pogonomyrmex s. str. comprises 

 some twenty species, spread over portions of the high arid plains 



