1883.] 



NATURAL SCIENCES OF PHILADELPHIA. 



35 



they are to be looked for in the Mexican region of the Neotropical 

 realm, I give a list of these genei-a, with a corresponding one 

 of the Mexican region, to illustrate the extent of the similarity 

 between the two regions. 



B. Sonoriana. 



Plagopterinae, 



Heloderraa. 



Crotaphytus. 



Uta. 



Uma. 



Callisaurus. 



Gyalopinm. 

 Phimothyra. 

 Trimorphodon. 

 Hj^psiglena. 



Pisces. 



Reptilia. 



Lacertilia . 



R. Mexicana. 



Heloderma. 



Ophidia, 



Ficimia. 

 Phimothyra. 

 Trimorphodon. 

 Hypsiglena. 



It seems then that the Neotropical relationships of the Sonoran 

 region are not great. In this consideration I have omitted the 

 genera which are common to the Mexican region and the Nearctic 

 realm in general. Such are Eanidse^ Gnemidophorus, Sceloporus, 

 Bascanium, Tropidonotus, Eutsenia, Pityophis, Spilotes, Ophiholus 

 and Elaps. These forms serve to indicate the affinity between 

 the Nearctic realm and the Mexican region. The line between 

 the two is, however, not 3'^et exactly drawn. The former extends 

 on the west coast at least as far south as Guaymas, and on the 

 plateau 'as far as Guanajuato. On the east coast the Neotropical 

 fauna reaches near to the Rio Grande. See On the Zoological 

 Position of Texas, by the writer, in Bulletin U. S. National Museum, 

 No, ^20, August, 1880; and Eleventh Contribution to the Her- 

 petology of Tropical America, by E. D. Cope, Proceedings Amer, 

 Philosoph, Society, 18t9, p. 267, 



