200 



WILLIAM MORTON WHEELER. 



habit but live on insect food. The clypeal and mandibular am- 

 mochaetae are smaller than in the palearctic species. There are 

 no hairs on the mentum, but the gular bristles are long, 

 arcuately inserted, rather stiff, directed downward and but little 

 curved. The development of these, as well as that of the cly- 

 peal and mandibular ammochsetae varies directly as the aridity of 



Fig. II. Myrmecocystus melliger orbiceps sp. nov. 



the region inhabited by the ants. Thus M. mexicanus var. horti- 

 deorum McCook (Fig. 10) which lives on the high plains in com- 

 paratively humid regions, has very poorly developed clypeal and 

 mandibular bristles and the gular ammochaetae are rather short. 

 In M. melliger orbiceps subsp. nov. (Fig. n) which inhabits' the 

 drier regions of central and western Texas, all of the bristles are 



Fig. 12. Myrmecocystus melliger semirufus Emery. 



longer. Finally M. melliger semirufus Emery (Fig. 12), a small 

 form peculiar to the sandy spots in the dry deserts of Arizona 

 and southern California, surpasses all the other American forms 

 in the development of the ammochsetae. 



The uniform presence of mental ammochaetae and the larger 

 size of the males in the Old World forms of Myrmecocystus would 



