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PROCEEDINGS OF THE NATIONAL MUSEUM 



PLECOTUS ( CORYNORHINUS l 

 USNW 297218 



POSTERIOR 



PLECOTUS ( CORTNORHINUS ) TOWNSENDII LOBE 



CM 18760 



PLECOTUS ( PLECOTUS ! AURITUS 

 USNM 18487 



Figure 5. — Comparison of the presternum of three species of Plecotus. Ventral (left) and 

 lateral (right) aspects. Camera lucida sketches. 



phyllotis, although the anterior nares are not enlarged m the latter 

 species. 



The zygomatic arches show progressive reduction and weakening 

 through the series from relatively heavy and strong in P. phyllotis 

 and P. auritus to relatively light and weak in P. townsendii. Also, 

 in the latter species there is a shift of the postorbital expansion of the 

 zygoma from its primitive median position to a posterior location. 



The median postpalatal process, absent in P. phyllotis, is slightly 

 developed in P. auritus, and is a prorainent spine in P. mexicanus and 

 in some forms of P. townsendii. The lateral grooves ("basial pits") 

 commencing in the basioccipital and ending abruptly in the basisphe- 

 noid are prominent in P. townsendii; they are ill-defined or absent in 

 the more primitive P. phyllotis and P. auritus. Slight elongation of 

 the auditory bullae is a specialization peculiar to P. phyllotis. The 



