1987] 
Shattuck — Pogonomyrmex occidentalis complex 167 
County (33%), Idaho. Thus neither of these characters fully sup- 
ports the distributional boundaries of P. salinus and P. owyheei 
cited by Cole (1968): PetDor indicates the northern extent of P. 
salinus as central Oregon rather than southern Oregon, while the 
southern boundary of P. owyheei (northern California and Nevada) 
is supported; PpDor supports the northern extent of P. salinus as 
southern Oregon but indicates P. owyheei as occurring throughout 
Nevada rather than limited to the northern portions. 
All specimens of P. montanus have PetDor state 5 and PpDor 
state 5 (Table 1), thus showing no geographic variation. P. subden- 
tatus does show variation in these characters, with PetDor states 1, 
3, 4 and 5 represented as well as all PpDor states (Table 1). How- 
ever, this variation is distributed randomly throughout the range of 
the species (Figs. 29 and 30). 
Venter of Petiolar Peduncle (PetVent) 
In P. occidentalis, all states of PetVent are represented (Table 1). 
This agrees with the findings of Cole (1968), except for the presence 
of a prominent process (states 5 and 6) in 24% of the specimens from 
Dawson, Roosevelt and Rosebud counties, Montana. 
Pogonomyrmex owyheei possesses the first five states of PetVent 
in decreasing frequency and lacks the sixth state (Table 1). P. salinus 
shows a similar trend, but possesses all states (Table 1) and a higher 
proportion of individuals with higher states. P. subdentatus has all 
states represented but in increasing frequency from state 1 to state 6 
(Table 1). The presence of a large process on the venter of the 
petiolar peduncle is often used as a diagnostic character for P. sub- 
dentatus (Creighton, 1950; Cole, 1968) and the presence of states 4, 
5 and 6 in populations of P. salinus in western Nevada may indicate 
gene flow between these two species. States 4, 5 and 6 occur in P. 
salinus only in or near areas containing populations of P. subdenta- 
tus (south central Oregon, western Nevada), while in all other areas 
P. salinus exhibits states 1, 2 or 3 (Fig. 31). Other characteristics of 
P. subdentatus (cephalic sculpturing, propodeal spine develop- 
ment, thoracic profile) do not appear in western Nevada popula- 
tions of P. salinus, indicating only limited or no gene flow between 
P. salinus and P. subdentatus. There is a weak trend for state 1 to 
increase and states 2 and 3 to decrease as one moves outward from 
northwestern Nevada. 
