1922] Schmidt, Amphibians and Reptiles of Lower California 629 



genus Sotor, now entirely restricted to islands in the Gulf of California. 

 Ufa thalassina, restricted to southern Lower California, also may be 

 placed with this "older" element. Finally, the species common to the 

 Cape district and the San Diegan district are believed to represent a 

 radiating migration antedating the present conditions, as it is difficult 

 to see how migration from the relatively humid San Diegan area to the 

 restricted similar areas in the Cape district could take place at present, 

 on account of the intervening deserts. It must therefore be supposed 

 that a continuous, or nearly continuous, semi-humid belt connected the 

 San Diegan and the Cape areas at an early date. It is not incompatible 

 with this theory that, in the diverse habitat conditions of Lower Cali- 

 fornia and its isolated position, a large number of species have developed 

 "in place." This differentiation after migration accounts in part for the 

 distinctive species of the various faunal districts. 



ARTIFICIAL KEYS TO THE GENERA OF AMPHIBIANS AND REPTILES 

 IN LOWER CALIFORNIA 



The amphibians are scantily represented in Lower California by 

 eleven species of seven genera, which may be recognized as follows: 



1. Adult tailed 2. 



Adult tailless 4. 



2. Toes four in front, five behind 3. 



Toes four on each foot Batrachoseps. 



3. Tail longer than head and body ; size large, adult exceeding 10 inches . . Plethodon. 

 Tail shorter than head and body; size smaller, adult rarely exceeding 6 inches. 



Aneides. 



4. Digits dilated at the tip Hyla. 



Digits not dilated 5. 



5. Skin smooth Rana. 



Skin more or less warty 6. 



6. Two metatarsal tubercles, not black or horny Bufo. 



A single (inner) metatarsal tubercle with a black and horny edge. .Scaphiopus. 



The two species of Hyla may be distinguished as follows : 



Skin rough, with small warts; two phalanges of fourth toe free from web. 



H . arenicolor 

 Skin smooth, three phalanges of fourth tee free frcm web H. regilla 



The two species of Bufo do not occur in the same area; they are 

 very different in form, the Bufo boreas halophilus in the northwestern 

 part of the peninsula being a large species with a deep head, the Bufo 

 punctatus from the cape region much smaller, with a flattened head. 



