24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 



topography or the usual geographical barriers of mountain ranges, 

 rivers, etc., is that inhabited by the other two western subspecies. As 

 well as possessing an extremely wide and geographically variable 

 range, h. adelpha presents relatively great morphological variation, 

 particularly in the male (figs. 29-31), as compared to the variations 

 found within any of the other subspecies (figs. 7, 10, h. hesperomys; 

 18-20, h. ravalliensis ; and 17, h. pacifica). These variations cannot be 

 correlated with distribution and, in fact, are exhibited in a series taken 

 from the same individual host. 



Intergradations between h. adelpha and h. hesperomys, as may be 

 expected, occur in the plains area of western North and South Dakota 

 and eastern Wyoming near the South Dakota border. In these par- 

 ticular regions neither true h. hesperomys nor typical h. adelpha have 

 as yet been found. No intergrades between the other subspecies have 

 been recognized during the course of this study. In this regard, it is 

 pointed out that in the Dakota regions there are no isolating factors 

 which would prevent intergradation and hybridization. 



PEROMYSCOPSYLLA EBRIGHTI (C. Fox, 1926) 



Figures 38-42, 109, no 



Leptopsylla ebrighti C. Fox, Pan-Pacific Ent., vol. 2, p. 182, figs. 3, 4, 1926. 

 Ctenopsylla ebrighti Wagner, Akad. Nauk S.S.S.R. Zool. Inst., Parazitol. 



Sbornik (Mag. Parasitol. Mus. Zool. Acad. Sci.), Leningrad, vol. i, p. 147, 



1930. 

 Peromyscopsylla ebrighti Jellison and Good, U. S. Publ. Health Serv., Nat. 



Inst. Health Bull. 178, p. 121, 1942. — Hubbard, Fleas of western North 



America, p. 335, 1947. 



Head. — Similar to hesperomys except: female with three or four 

 spiniforms opposite frontodorsal angle; genal lobe (fig. 38, G.L.) less 

 than one-half length of lower genal spine ; second antennal segment 

 with marginal bristles not reaching beyond second segment of club in 

 male and about one-half length of club in female. 



Thorax, — Essentially as in hesperomys except lacking erect bristles 

 dorsally on mesonotum. 



Abdomen. — As in hesperomys. 



Male. — Eighth tergum mediolaterally with two rows of two to 

 three long bristles each. Eighth sternum (fig. 39) with caudal margin 

 ventrally emarginate, producing broad dorsal lobe bearing three apical 

 bristles, one of these shorter than others ; ventrally with one or no 

 bristles; membranous process (M.P.) very small. Immovable process 

 of clasper (fig, 41, P.) with bluntly rounded apex; characteristic 

 bristle on posterior margin not as long as width of digitoid. Digitoid 



