60 
Psyche 
[June 
basis alone, be unable to utilize stations on the Mexican 
plateau or similar areas to the north of it. I do not for 
one moment maintain that elevational range is the only 
factor that restricts pima to the Sonoran Desert region 
but it would surely seem to be one of the more important 
factors which go to determine this range. 
I wish now to consider the habits of imberbiculus and 
pima. It is much to be regretted that Wheeler did not 
content himself with the excellent account of the habits 
of imberbiculus which he published in 1902 (7). All the 
nests on which Wheeler’s original account was based were 
found under stones and each nest contained very few 
workers. Beneath the stones Wheeler discovered small 
chambers containing unhulled seeds and others full of 
brood. When transferred to artificial nests the imber- 
biculus workers made no effort to utilize the seeds as 
long as they were supplied with insect food. But when 
the supply of insect food was cut off the workers hulled 
the seeds and not only ate them but also fed pieces of 
them to the larvae. Wheeler was soon aware (8) that 
his original nests of imberbiculus had been exceptional 
in that they were built under stones, for he discovered 
other colonies at San Angelo, Texas, where the nests 
were free in the soil and surmounted by small craters. 
But it may be said that at the start Wheeler presented 
a very accurate picture of the nesting habits of imber- 
biculus. It is, therefore, difficult to explain why he 
obscured this picture in 1910 (9) by grouping imber- 
biculus and pima with other species of Pogonomyrmex 
with which they have little or nothing in common. In 
his celebrated volume Ants (page 283) Wheeler makes 
the following observation: 
“1. P. subdentatus, apache , sancti-hyacinthi and deser- 
torum and Ephebomyrmex imberbiculus , townsendi and 
pima. These are small species confined to the deserts of 
Texas, New Mexico, Arizona, Californa and northern 
Mexico. Their colonies are always insignificant and widely 
scattered, comprising only a few individuals. The nests 
are small, obscure craters, 10-20 cm. in diameter and a 
