1907.] Wheeler, Fungus-growing Ants of North America. 761 



6. Atta (Mycetosoritis) hartmanni sp. nov. 



This interesting little ant was discovered May 9, 1903, in the sandy 

 country on the left bank of the Colorado River at ^lontopolis and Delvalle, 

 near Austin, Texas, while, with the assistance of ]\Ir. C. G. Hartmann, I 

 was examining and photographing the nests of Trachymijrmex turrijex 

 and sepientrionalis. At first I was inclined to regard the diminutive workers 

 as merely belonging to incipient Trachymyrmex colonies, but closer study 

 soon showed that these little ants were not only specifically distinct but also 

 represented a new and interesting subgenus, in certain respects intermediate 

 between Trachymyrmex and Cyphomyrmex. There were hundreds of 

 their nests, often within a few decimeters of one another, in the fields or in 

 clearings among the oaks and wherever the sand was fully exposed to the 

 sun. These regions were also inhabited by several species of solitary wasps 



Fig. 26. Crater of Atta (Mycetoiioritisj hartmanni from sandy post-oak woods at Monto- 

 polis, Texas. Natural size. (Pliotograpli by Mr. C. G. Hartmann.) 



(Microbemhex and Pompilus) and numerous colonies of ants {Trachymyrmex 

 turrijex and septentrionaUs, Aphaniogaster treata', Pheidok splendiclula and 

 morrisi, Solenopsis geminata, Pogonomyrmex comanche, PrenoJepis arenivaga, 

 etc.). The herbaceous flora of the region consisted of a sparse growth of 

 bull-nettles (latropha stimulosa), showy gaillardia {GaiUardia pukhella), 

 butterfly weed (Asclepia.s' tuherosa), white prickly poppy {Argemonc alba), 

 .stone crop (Sedum) and cactus (Opuntia engelmanni), all in full bloom. 



The nests of the Mycetosoritis are small turriform craters of i)ure sand 

 5-8 cm. in diameter at the base and tapering rapidly to the summit, which 

 is 2.5—4 cm. high and perforated with a circular orifice barely 2 mm. in 

 diameter (Fig. 26). Occasionally the summit is double (PI. L, Fig. 28) 

 and furnished with two entrances, which, however, soon unite to form a 



