332 Bulletin American Museum of Natural History. [Vol. XXII, 



and pebbles have been washed into crevices or depressions or under 

 rocks in the boulder beds of the streams. 



As ants, with the exception of certain peculiarly modified desert 

 species, are intimately dependent on moisture, we find that most 

 of the species collected occur in the Kohonino Forest and about 

 Willow Creek in the Indian Garden. But the species of these two 

 localities, separated by an altitude of about 3400 feet, are almost 

 entirely different: those on the Kohonino Plateau belonging to the 

 general Rocky Mountain fauna of the same or similar altitudes 

 (6000 to 8000 feet), whereas those of the Indian Garden are in large 

 part identical with the species of the warmer and moister spots in 

 Texas and New Mexico. The Kohonino fauna extends down sparingly 

 on the walls of the canon to the lower limit of coniferous trees at an 

 altitude of about 4500 feet. The Formicidae of the Angel Plateau 

 and lower portions of the canon to the river belong, like the flora, to 

 well-known desert species widely distributed through western Texas, 

 the southern portions of New Mexico, Arizona and California and 

 the adjoining portions of Mexico at corresponding elevations. We 

 may therefore distinguish the following four faunal zones in the 

 distribution of the Formicidae of the canon: 



1, The fauna of the rim and canon walls from about 7000 feet 

 down to an altitude of about 4000 feet. The most characteristic 

 species of this zone is the "Occident ant" of McCook {Pogonomyrmex 

 occidentalis) . The list of species comprises the following: 



Monomorium minimum, Dorymyrmex pryamiciis, 



Cremastogaster lineolata, Tapinoma sessile, 



Pheidole ceres, Lasius americanus, 



Myrmica scabrinodis, Formica moki, 



Pogonomyrmex occidentalis, Formica argentata, 



Leptothorax nitens, Formica neoruflbarbis, 



Leptothorax neomexicanus, Formica subpolita, 



Liometopum luctuosum, Camponotus nitidiventris, 



Cam-ponotus maccooki. 



2, The Indian Garden fauna, which is in all probability repre- 

 sentative of all the other humid spots in the canon at the same 

 elevation. This fauna comprises the following species: 



Ponera opaciceps, Dorymyrmex pyramicus, 



Myrmecina brevispinosa, Iridomyrmex analis, 



Monomorium minimum, Nylanderia imparis, 



Pheidole vinelandica, Lasius americanus, 



AphcBnogaster texana, Formica gnava. 



3, The fauna of the Angel Plateau and the adjacent dry boulder 



