1907.] 



Wheeler, Fungus-gromng Ants of North Av^erica. 



743 



2. Atta (Mcellerius) versicolor Pergande. 



This ant is unquestionably a ^Mexican species which enters the United 

 States only along its southwestern frontier where it inhabits the arroyo 

 bottoms in the most arid regions. I have observed the tj^ical form of the 

 species only in two localities, at Tucson, Arizona, and at Yucca in the same 

 state, a few miles east of the Californian boundary. At Tucson several 

 colonies were found in an arroyo near the Carnegie Desert Botanical Labora- 



Fif<. 17. One of tlie critlers ol tlie gioiiij leiJiesented in the ijrecedinf; ligure, about i 

 natural size, showing the difference between the pellets brought up bj' the ants and the surround- 

 ing soil. (Photograph by the author.) 



tory where the soil was probably .somewhat moist at a depth of .several feet, 

 but where the surface was very hard and dry and covered with typical desert 

 ]ilants such as the retama (Parkinsonia), the small acacia known as "cat- 

 claw" or "una de gato" {Acacia grce/gi), the Mexican grease-wood {CoviUora 

 Iridentata), the ocotillo {Fourpiicra .splendenfi) and .several cacti (Opiiniia). 

 At Yucca the ants occur in similar arroyos bordered with the beautiful pod- 

 willows {Chilopsis mlir/)ia) in the midst of a very hot, dry desert, studded 



