208 BULLETIN 17 5, UNITED STATES NATIONAL MUSEUM 



and affinis; d. deppei became separated from affinis in the south and 

 in turn gave rise to d. jani and lineaticollis ; vertebralis was separated 

 from the southern group of affinis by the invasion of the Gulf of Cali- 

 fornia, and spread north through Lower California and southern 

 California; and the subspecies of catenifer, with c. deserticola as the 

 stem form, appeared to the north and west of affinis. 



The probable affinities and lines of dispersal of the various forms 

 of the genus, in accordance with this explanation of the evolutionary 

 development of the genus, may be illustrated by the following diagram: 



catenifer 

 \ 



\ 

 deserticola 



/■• 

 >/ 

 annectans melanoleucus 



affinis /" 



(northern) / 



vertebralis sayi »ruthvcni »lodingi 



affinis \ 



(southern) \ 



mugitus 



deppei 

 \ 

 jani 



lineaticollis 



