614 Bulletin American Museum of Natural History [Vol. XLVI 



Of these, the water snake Natrix shows especial Mexican relations, 

 the same species occurring in western Mexico and Lower California. 

 Lichanura, Phyllorhynchus, and Chilomeniscus are nearly confined to the 

 peninsula, but range into southern California and southwestern Arizona 

 at the north. The distribution of Trimorphodon lyrophanes appears to be 

 discontinuous, a wide gap separating the records in southern Arizona from 

 the Lower Calif ornian localities, a distribution paralleled by Phrynosoma 

 solare among the lizards. The single species of Elaphe is also without a 

 representative in either the San Diegan or Colorado Desert faunae, 

 its nearest relative geographically being west Mexican. The twelve re- 

 maining genera are all wide-ranging North American forms. Tham- 

 nophis enters Lower California from the North and is absent from the 

 southern end of the peninsula, as probably also is Rhinocheilus. 



The single fresh-water turtle is apparently closely related to the 

 Mexican species, Pseudemys ornata. 



To repeat, of the thirty-eight genera of reptiles in Lower California, 

 six are absent in the Pacific area and in the Sonoran deserts of the 

 United States, and by their presence in western Mexico, as allied or 

 identical species, suggest a "Mexican element" in the Lower Calif ornian 

 fauna; these genera are Ctenosaara, Sator, Bipes, Natrix, Elaphe, and 

 Pseudemys. The three last are widespread in North America, and their 

 absence in the Sonoran deserts of the United States is due to absence of 

 suitable habitat conditions. The aquatic forms may have entered the 

 peninsula directly from Mexico, though this is improbable. Their 

 northward range on the coast of Sonora is, unfortunately, not satis- 

 factorily known. Ctenosaura is a characteristically Mexican and Central 

 American genus. A species reaches the Arizonan border from Mexico, 

 and it is not impossible that the genus may formerly have ranged farther 

 into the Sonoran deserts to the north and so may have found access to 

 Lower California, where subsequent isolation is shown by the specific 

 distinctness of the west Mexican and Lower Californian forms. Bipes 

 and Sator I regard as examples of relict distribution, their present re- 

 striction being due to the extinction of the intermediate Sonoran forms. 

 The genus of geckos, Phyllodactylus, has a characteristically erratic 

 distribution, and not much importance can be ascribed to its presence 

 in both Lower California and Mexico. P. tubercidosus has recently been 

 discovered in southern California. Without knowing the relations of 

 Elaphe rosalise within the genus, it is impossible to form an opinion as to 

 its geographic relations. It is not improbable that it belongs with 

 Ctenosaura in the history of its distribution. The range of certain other 



