1914] W heeler—Harvesting Ants io 
base is opaque and finely punctate-striolate. These differences are 
all so slight that hwachucanus may eventually prove to be merely 
a subspecies of bispinosus. The resemblances between the two 
forms, separated by such a wide territory, is very suggestive in 
connection with the origin of the genus Pogonomyrmex. Owing 
to the fact that this genus is represented by the greatest number 
of species in North America, and that it is most closely related to 
the boreal genus Myrmica, it has been assumed that the species of 
Pogonomyrmex originated in the western United States and mi- 
grated thence along the arid plains and mountain ranges through 
Mexico, Central and South America as far as Patagonia. On this 
assumption, P. hwachucanus might be regarded as a rare relict of 
a group of species which once ranged over a large portion of west- 
ern America, but now survive only in Chili and the Huachuca 
Mountains of Arizona. 
P. huachucanus and guatemaltecus, together with bispinosus and 
two other South American species, brevibarbis Emery and silvestrit 
Emery, are also of considerable interest, because in the restricted 
area of the gula enclosed by the long hairs of the psammophore 
and in sculpture they are transitional between the species of Pog- 
onomyrmex sens. ste. and the subgenus Ephebomyrmex Wheeler. 
The acute, spinose character of the metasternal angles in brevi- 
barbis and silvestrii reveals a still closer relationship to the latter 
subgenus. All of these species may, therefore, represent today 
the most primitive and ancestral forms from which both subgenera 
have been evolved. 
3. Pogonomyrmex californicus Buckley. 
The worker of the typical form of this species measures 5.5—6 mm. and is charac- 
terized by the shape of the petiole and the sculpture. The anterior surface of the 
petiolar node forms very nearly a right angle with the upper surface of the peduncle, 
and the ventral surface of the latter bears no tooth. The surface of the body is 
shining, the rug of the head and thorax being sharp and pronounced, the spaces 
between them impunctate or with punctures so small and shallow as to be barely 
visible under a magnification of 20 diameters. The petiolar and post-petiolar nodes 
are very finely and densely punctate and indistinctly rugulose. The body is light 
ferruginous red, the mandibles, clypeus and legs more yellowish. 
The female measures about 8 mm. and resembles the worker very closely in form, 
sculpture and color. The head is somewhat broader than long. Wings hyaline, 
with their basal portions distinctly yellowish, the veins and stigma brown. 
The male measures 7.5 mm. and has rather broad mandibles, with oblique 4- 
toothed blades. Head, thorax, nodes of petiole and postpetiole, coxze and femora, 
