224 
Psyche 
[December 
Twin Falls, occupying small, flat crater-nests of fine sand, 
in open areas of the sagebrush semidesert, and occasionally 
on the faces and in the denuded areas of mounds of Pogono- 
myrmex occidentalis Cresson. 
18. Tapinoma sessile Say 
Large colonies of this very common and well known ant 
are beneath rocks in moist places. Winged sexes appear in 
late June at Twin Falls. 
19. Iridomyrmex pruinosus var. 
Populous colonies of very active workers of an un- 
described variety of pruinosus were found near Hagerman, 
inhabiting aggregated crater nests of fine sand in an area 
of greasewood. 
20. Lasius niger americanus Emery 
This very common occupant of the more moist areas 
throughout the state, nests beneath fallen timber or rocks, 
and more rarely occupies small, rude crater-nests of earth 
or sand. The workers are abundant and much brood develops 
into winged forms throughout June, July and August, de- 
pending upon the location of the nests. The ants are secre- 
tivorous and in some cases also scavengeristic. 
21. L. niger sitkaensis Pergande 
Although less common than the variety, americanus, sit- 
kaensis is, nevertheless, a rather frequent occupant of moist 
places. Its nests and habitats are almost identical with 
those of americanus. 
22. L. umbratus mixtus aphidicola Walsh 
This variety lives beneath stones in very moist areas 
throughout the Snake River Plains. Its food consists chiefly 
of secretions from aphids and coccids which are attended in 
the nests. 
23. Polyergus rufescens breviceps Emery 
Only one nest of this species, which contained many work- 
ers of Formica fusca subsericea \ was observed by the writer. 
^lave complex. 
