1922] Schmidt, Amphibians <n/rf Reptiles of Lower California G13 



peninsula, may be considered as directly derived from the Colorado 

 Desert. .4. nniella enters the peninsula only a short distance on the Pacific 

 side. The remaining twelve genera reach the southern part of the penin- 

 sula. Yerticaria is nearly confined to Lower California, ranging to the 

 north only a short distance into the San Diegan area. Of the remaining 

 eleven genera, Dipso-saurus, Sauromalus and Callisaurus form a group 

 whose distribution is very similar, ranging through the whole of Lower 

 California except the northwestern part, the Colorado and Mohave 

 deserts in California, southern Nevada, extreme southwestern Utah, 

 and southwestern Arizona, entering Sonora probably in the desert areas 

 bordering the Gulf of California. Xantusia, with a restricted distribu- 

 tion in California, is represented by a distinct species (X. gilberti) in 

 southern Lower California, by one in the San Diegan area (X. hen- 

 shaivi, not yet recorded from Lower California), and by one in the 

 Mohave Desert (X. vigilis) which enters northeastern Lower California. 

 X. gilberti appears to be most closely related to the Mohave Desert 

 species. 



The remaining genera have a wide distribution in North America. 

 Of Crotaphytus, only the widely distributed C. wislizenii reaches southern 

 Lower California. The Lower Calif ornian Plestiodon is scarcely distinct 

 from the northern P. skiltonianus, which is a Pacific form. Gerrhonotus 

 has a distinct species in southern Lower California and one in the San 

 Diegan area, while it is also absent from the Colorado Desert, reappearing 

 on the Mexican plateau. Sceloporus, Uta, Phrynosoma, and Cnemido- 

 phorus, each with several species in the peninsula and others on the 

 adjacent islands, are the best developed genera in the fauna of Lower 

 California. Each has one or more species confined to the southern 

 part of the peninsula. Uta is remarkable for the two species, Uta thalas- 

 sina and Uta mearnsi, respectively of the southern and northern half of 

 the peninsula. If mearnsi were extinct, thalassina could be considered 

 as forming a distinct monotypic genus; but mearnsi is so exactly inter- 

 mediate between thalassina and typical Uta that it is impossible to place 

 it with either. 



The eighteen genera of snakes in Lower California are the following. 



Siagonodon Rhinocheilus 



Lichanura Hypsiglena 



Coluber Natrix 



Salvadora Thamnophis 



Phyllorhynchus Sonora 



Elaphe Chilomeniscus 



Arizona Tantilla 



Piluophis Trimorphodon 



Lampropeltis Crotalvs 



