66 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 



L.L. are apparent only when the distolateral lobes are inclined ventrad 

 (figs. 105, 106) ; at such times the rolled connecting portions may be 

 visible (fig. 105, ROLL). The various relative positions of these 

 structures are illustrated for P. hesperomys (figs. 104-106), P. cata- 

 tina (figs. Ill, 112), and P. ebrighti (figs. 109, no). 



The distolateral lobes reach their maximum development in the sub- 

 species of P. hamifer and P. ostsibirica longiloba. There the struc- 

 tures are not only relatively enormous in size, but are modified so as 

 to possess a heavily sclerotized, more lateral, horseshoe-shaped portion 

 bearing the central thickening (C.TH.). 



P. tikhomirovae, in addition to having very small distolateral lobes 

 and large unmodified lateral lobes (fig. 121, L.L.), is also unspecial- 

 ized in that the crochets are of the type characteristic of the Leptopsyl- 

 linae in general — very large structures longer than the end chamber — 

 here three times as long as broad and apically subrounded, with a 

 median lateral acuminate rib (CR.). In P. silvafica the crochet is of 

 a similar shape (fig. 113, CR.) but only a sagittate or acuminate scle- 

 rotization is readily visible, the crochet outlines (CR.O.) being semi- 

 membranous. The sagittate rudiment is probably the homologue of 

 the median lateral rib of tikhomirovae. In the other Peromyscopsylla 

 the crochet is even more reduced — the crochet outlines, too, are un- 

 apparent. In P. selenis (fig. 114, CR.) only the crochet base and 

 ventral portion are sclerotized. P. himalaica (fig. 115) shows further 

 reduction in that much of the base is semimembranous. The rib rem- 

 nant or crochet vestige is somewhat dagger-shaped in P. hesperomys 

 (fig. 104), ebrighti (fig. no), draco (fig. 108), and catatina (fig. 

 112) ; but subsagittate ^ in hamifer (figs. 117, 118), ostsibirica longi- 

 loba (fig. 119), and bidentata (fig. 120). The crochets of P. selenis 

 (fig. 114) and himalaica (fig. 115) are apically somewhat spatulate. 

 Reduction has proceeded even farther in scotti (fig. 107), where only 

 a portion of the base of the crochet remains. 



The lateral lobes are well developed but relatively unspecialized in 

 P. tikhomirovae (fig. 121, L.L.), scotti (fig. 107), ebrighti (fig. no), 

 silvatica (fig. 113), and draco (fig. 108). In P. hamifer (fig. 117), 

 ostsibirica longiloba (fig. 119), and bidentata (fig. 120), not only are 

 the lateral lobes even relatively larger but they are adorned with 

 definite characteristic spiculose or rugose processes. P. hesperomys 

 (fig. 104), however, is minutely spiculose. 



The lateral lobes are somewhat reduced in P. selenis (fig. 114), 

 catatina (fig. 112), and himalaica (fig. 115). It is of interest and 



3 As seen in the mounted specimen, i.e., lateral aspect. The dorsal view (slightly 

 askew) is illustrated in figure 116. 



