558 PROCEEDINGS OF THE ACADEMY OF [Aug., 



The Chihuahuan has given origin to no widely ranging snakes 

 except Crotalus and Sistrurus. Its great wealth of lizards has not 

 spread extensively into the Atlantic slope. Sceloporus and Cnemido- 

 phorus being represented there by but one species each; Eumeces by 

 one which reaches to Canada and perhaps two others more southern 

 and scarce in numbers; and the one species of Liolepisma, reaching to 

 New Jersey. 



That the Austroriparian fauna is the older of the two is made prob- 

 able by the geological age of the region, and certain by the character 

 of its forms, many of which belong to genera widely spread in the 

 Holarctic, others having obvious genetic relationship to these or to 

 other ancient forms. The separate identity of these two faunas, as 

 far back as they can be traced, confirms the conclusion already reached 

 from their present distribution, that the association of the Sonoran 

 with the Austroriparian into one transcontinental zone is unnatural 

 and cannot be maintained for reptiles. 



How far the stations occupied by reptiles conform to Dr. Merriam's 

 vertical zones, when the attempt is made to correlate these in widely 

 distant localities, can not now be determined. At a later time I hope 

 to examine this branch of the subject in some detail, but even with 

 the limited amount of information now available of the kind needed, 

 certain anomalies appear which do not seem open to explanation by 

 that theory. 



Indeed the proposition that all forms of life must conform to the 

 same areas of distribution accords with neither theory nor facts. It 

 may be, as stated by the distinguished author of transcontinental life 

 zones ,^^ and doubtless is, illogical to assume that a faunal and a floral 

 map must differ; but it is quite otherwise to assume as a working 

 hypothesis that they may do so, and when organisms differ as widely 

 in physiological adaptations as reptiles, for instance, do from mam- 

 mals, the assumption that their reactions to the same conditions of 

 environment must be similar, certainly is not far from likeness to a 

 well-known logical fallacy. 



While there can be no doubt of the controlling influence of tempera- 

 ture upon the distribution of reptiles as a class, it is c^uite certain that 

 moisture plays a more important part in regulating the range of its 

 genera and species than is the case with either mammals or birds, 

 especially when their limited powers of migration are considered. 



The details of their distribution in the southern divisions of the 

 Medicolumbian sufficiently show its potency. 



" No. Am. Fauna, No. 3, p. 27. 



