22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 



species in the far western United States and Canada, published during 

 recent years, have surprised workers in the field. This experience has 

 been duplicated with another characteristic flea of eastern Peromyscus, 

 Orchopeas Icitcopus (Baker, 1904), which has been taken in Utah, 

 Texas, Arizona, Nev/ Mexico, California, and even Chihuahua, 

 Mexico (unpublished records of authors). 



The subspecies of Peromyscopsylla hcspcromys present a very inter- 

 esting problem in regard to their various morphological and distribu- 

 tional patterns. Dr. Karl Jordan, F.R.S., has previously noted the 

 interesting fact that subspeciation of fleas from north to south does not 

 occur in the eastern part of North America, whereas the same species 

 may form several variants both from north to south and from east to 

 west in the western part of North America (Jordan, 1928). The 

 pattern presented by hesperomys is an excellent example of this fact 

 in that h. hesperomys from Tennessee or the Carolinas is indistinguish- 

 able from h. hesperomys taken in New York or the New England 

 States. Western hesperomys has, on the other hand, formed three 

 subspecies recognizable on morphological grounds. The geographic 

 distribution of these subspecies is rather puzzling. P. h. pacifica, found 

 mainly on Peromyscus, is apparently confined to the western slopes 

 of the Cascade Range (Oregon and Washington) and the coastal 

 mountains of British Columbia. P. h. ravalliensis seems to be typically 

 found on Neotoma in the western slopes of the northern Rocky Moun- 

 tains, including the Monachee Mountains of eastern British Columbia, 

 the Bitterroot Range in western Montana, perhaps as far south as the 

 Wasatch Mountains in northeastern Utah (Utah range based on one 

 specimen, a female, from Neotoma, Cache County, doubtfully deter- 

 mined as h. ravalliensis by the authors), and reaching the Blue Moun- 

 tains of northeastern Oregon and the Salmon River Mountains of 

 Idaho based on Hubbard's interesting records from Neotoma, Wal- 

 lowa Lake, Oreg. The range of these two subspecies is understandable 

 for both ecological and geographical reasons, i.e., mountain barriers 

 and host differences. P. h. adelpha, undoubtedly a morphological entity 

 has a far greater range than the above forms despite the natural bar- 

 riers involved. This subspecies is found in the coastal range of Cali- 

 fornia; in the Sierras of California and Nevada on both eastern and 

 western slopes, in the southern Rocky Mountains on both eastern and 

 western slopes (Arizona, Utah, New Mexico, Colorado, Wyoming), 

 and on the plains of Texas, Colorado, Nebraska, and Alberta. Two 

 females which may be this subspecies were taken in Michoacan, 

 Mexico, a very southerly record. The only western area (west of 

 about the 103d meridian) not occupied by h. adelpha, regardless of 



