556 PROCEEDINGS OF THE ACADEMY OF [Aug., 



in the absence of the Chihuahuan species Crotaphytus wislizeni, Uta 

 stansburiana, Sceloporus spinosiis clarkii, Cnemidophorus perplexus 

 and Crotalus molossus, none of which seem to range east of the Pecos. 



This large number of pecuhar species quite justifies the setting 

 aside of a Texan district, but the overwhelming proportion of its 

 Sonoran forms relegates it to that subregion, and not to the Austro- 

 riparian, with which it was finally associated by Cope. 



The boundary thus determined between the Austroriparian and 

 Sonoran subregions corresponds closely to that given by Merriam" 

 to his Humid and Arid divisions of the Lower Austral, and it remains 

 only to inquire into the reciprocal relations of the reptiles inhabiting 

 these areas. 



The Chihuahuan and Texan districts together share twenty-three 

 species with the Central, while of the sixteen which they have in com- 

 mon with the Austroriparian, five (Chrysemys elegans, Diadophis 

 amabilis, Ophibolus getulus sayi, Eutmiia proxima and Tantilla gracilis) 

 are also Central and only enter the western part of the Austroriparian. 

 Four more (Ciiemidophorus sexlineatus, Cyclophis cestivus, Liopeltis 

 vernalis and Ancistrodon coniortrix) are both Central and Eastern. 

 But seven species are therefore left common to and restricted to the 

 Sonoran and Austroriparian {Chrysemys mobilensis, Sceloporus spi- 

 nosus spinosiis, Tropidonotus clarkii, Tropidonotus rhombifer, Zamenis 

 flagellum flagellum, Flaps fulvius and Ancistrodon piscivorus), and of 

 these, four being aquatic are rendered in some degree independent 

 of the laws governing the migration of land forms. So far as their 

 species are concerned these two subregions have very little in common. 



Turning now to the genera recorded from Texas, twenty-five, found 

 in both subregions, are of such wide range in the Medicolumbian that 

 they are without l^earing on the present question and may be left out 

 of consideration. 



The following Sonoran genera do not enter the Austi'oriparian: 



Crotaphytus C.B. Barissia 



Holbrookia C. Anniella 



Uta B. Glauconia 



Lysopticus Salvadora 



Phrynosoma C.B. Arizona 



Eublepharis Rhinochilus C. 



Hcloderma Contia 



Gerrhonoti's Hypsiglena C. 



Amphiardis 

 ^'^Proc. Biol. Soc. of Wash., Vol VII, p. 28 and map. 



