746 BuUctin American Museum of Natural History. \Yo\. XXIII, 



lying on the floor of the chamber and consisted of fine Icaf-pulp covered with 

 a briUiant white mycehum dotted with bromatia. No other chambers or 

 galleries could be found, and as the nest contained only about one hundred 

 workers, the colony must have been incipient or enfeebled by age or adverse 

 conditions. As we had spent a great deal of time excavating this nest, and 

 as the heat was intense, so intense, in fact, that it caused the gutta-percha 

 plate-holders of my photographing outfit to soften and crumple, we could 

 not command sufficient energy to excavate a larger and more typical nest. 

 Unfortunately my stay of only a few hours at Yucca did not suffice- for the 

 exploration of one of the much finer nests of that locality. Judging from 

 the single nest examined at Tucson, MwUerius versicolor resembles most 

 of the species of Acromyrmex described by Moeller, Tanner, von Ihering 

 and Forel in having only a single chamber and garden. 



My notes on the subsp. chisosensis are even more fragmentary. At 

 Terlingua, Texas, in the Great Bend of the Rio Grande, I found a few dead 

 workers of this form in a spider's web under a stone, but was quite unable 

 to locate the nest from which they came. Judge O. W. Williams, however, 

 brought me a number of fresh specimens from a nest in a dry arroyo at the 

 foot of the Chisos Mountains some miles southeast of Terlingua. Both 

 localities are in very arid deserts, riven with canons, though the vegetation 

 is of a different type from that of southern Arizona. The red quicksilver- 

 hearing soil supports a sparse growth of the sotol {Dasylirion texamim), 

 desert spurges (Euphorbia aniisyphilitica and lafropha spathulata) and 

 lechugilla (Agave lechugilla), and the steep caiion walls are spangled with 

 star-like resurrection plants (Selaginella lepidophylla) and xeroph\iic ferns. 

 Such a region, with an annual rainfall of barely 25 cm., is certainly a remark- 

 able environment for an ant compelled to subsist on fungi that can grow 

 only in a humid atmosphere, an ant, moreover, belonging to a group which 

 was probably first developed in the rain-forests of the tropics. 



3. Atta (Trachymyrmex) septentrionalis McCook. 



The species of Trachymyrmex form small colonies of at most two or 

 three hundred, and often of only a few dozen individuals, and are so timid 

 and retiring in their habits that they are readily overlooked unless their 

 nests happen to be numerous and close together. And even when numerous 

 the nests are not often seen as their earth-works disintegrate and their en- 

 trances are kept closed during considerable periods of the year. 



Our best known species, T. septentrionalis, is widely distributed over the 

 Gulf and South Atlantic States, the var. obscurior ranging from central 

 Texas to Florida and the typical form from Maryland to New Jersey. There 

 are no observations to show that either of these forms extends equally far 



