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[Vol. 94 
Geographically, this difference may be explained by the presence 
of large scape values in southern Nevada (Fig. 36). Over the north- 
ern portions of the range of these two forms the SI values vary 
between 70 and 82, with a mean of 74.2, while in the southern 
portions (Clark, Eureka, Nye, White Pine counties, Nevada, and 
Mono County, California) SI varies from 74 to 84, with a mean of 
77.8. This trend, however, is weak with large SI values occurring in 
some northern populations (i.e. SI = 82 in Lake County, Oregon) 
and small values in some southern populations (SI = 66 in Washing- 
ton County, Utah). 
Taxonomic Conclusions 
P. montanus MacKay 
P. montanus MacKay, 1980: 151 (W, M, F). Type Loc.: Hanna Flat, 4 km NW 
Fawnskin, San Bernardino Co., California, USA. 
P. montanus is known only from the San Bernardino Mountains 
of southern California. It is retained as a full species in this study. 
P. occidentalis (Cresson) 
Myrmica occidentalis Cresson, 1865: 426 (W, F). Type Loc.: Colorado Territory, 
USA. 
Myrmica seminigra Cresson, 1865: 427 (M). Type Loc.: Colorado Territory, USA. 
(Synonymy by Forel, 1886: 42.) 
P. opaciceps Mayr, 1870: 971 (W). Type Loc.: New Mexico, USA. (Synonymy by 
Forel, 1886:42.) 
P. occidentalis ruthveni Gaige, 1914: 93 (W, M, F). Type Loc.: James Canyon, Elko 
Co., Nevada, USA. (Synonymy by Olsen, 1934: 507.) 
P. occidentalis utahensis Olsen, 1934: 509 (W, M, F). Type Loc.: Zion National 
Park, Utah, USA. (Synonymy by Cole, 1968: 95.) 
P. occidentalis may be separated from all other species in the 
complex by the offset tooth at the basal angle of the mandible. As 
demonstrated by Colley (1962), all other known characters occur in 
P. owyheei, as well as P. salinus, and are of no value in distinguish- 
ing this species. In no case did I find intermediate specimens 
between this species and P. owyheei or P. salinus, contrary to the 
findings of Allred (1982). The characters used in this study further 
support the distinctness of this species. The characters Gaster, Pet- 
Dor, PpDor and Scape show a moderate degree of variation, but a 
