AMMOCHiET^E. I 99, 



palearctic forms the clypeal and mandibular ammochsetae are 

 well developed. The gular bristles, however, are vestigial, their 

 function being usurped by a fan-shaped tuft of long recurved 

 hairs on the mentum. It is a significant fact that the hairs of 

 this tuft are rather short in M. cursor Fonsc, a species which,, 

 according to Emery does not occur in Africa. 1 It belonged 

 originally to the central Asiatic fauna, but just after the glacial 

 period migrated into central and southern Europe. In the north 

 African forms {M. albicans Roger, viaticus Fabr., bicolor Fabr_ 

 (== viaticus desertoruin Forel), bicolor megalocola Foerster) the am- 

 mochsetae, especially those on the mentum, are longer (Fig. 8). 

 In M. bombycinus Roger, a typical Saharan species, the bristles 

 reach their highest development (Fig. 9), and there are also fringes 

 of long curved hairs on the third joint of the greatly elongated 

 maxillary palpi so characteristic of the ants of this genus. 



There seem to be only two American species of Myrmecocystus,. 



Fig. 9. Myrmecocystus Fig. 10. Myrmecocystus hortideorum McCook. 



bombycinus Roger. 



mexicanns Wesm. and mclliger Forel, but each of these has a 

 number of subspecies and varieties, still in part undescribed and 

 all confined to the arid plains and deserts of the southwestern 

 States and northern Mexico. Some of the forms of each of the 

 species collect the secretions of plants and the ejecta of aphids 

 and store the liquids thus obtained in the replete workers ("honey 

 ants "). Other subspecies and varieties do not seem to have this 



1 " Rassegna Critica delle Specie Paleartiche del Genere Myrmecocystus," Mem- 

 R. Accad. Sci. Lt. Bologna, 1906, pp. I— 17, 35 figs. 



