56 NATURAL SCIENCE. July, 



Palaearctic Region, eighty-one, or over 70 per cent., are typically 

 Sonoran, while only two are typically Boreal. That as many as 

 thirty genera should range over the whole continent may be urged in 

 support of the retention of the Nearctic Region intact. Yet many 

 undoubtedly Neotropical genera range into the Sonoran ; and when 

 we consider the great extent of the North American continent and 

 the absence of any natural barrier to check migration from south to 

 north, our surprise should be that the mixing of the two faunas has 

 not been more complete. 



The second column of the summary given above yields highly 

 suggestive facts. With the single exception of Astur, all the fourteen 

 typical Boreal genera common to North America and the Palaearctic 

 Region are confined to the latter region in the Old World. This 

 shows most strongly the affinity between the Boreal American and 

 Palaearctic bird faunas. On the other hand, we find that of the 

 remaining forty genera in the second column, only three (Acredula, 

 Nyctala, and Archihnteo) are, in the Old W^orld, typically Palaearctic. 

 The rest are either of very wide range, or occur in both the Palaearctic 

 and Neotropical Regions. 



Strong confirmation of the distinction between the Boreal and 

 Sonoran faunas in America can be obtained from other groups. 

 The paucity of Lizards in the former fauna has indeed been 

 well shown by Dr. W^allace himself, as a survey of the tables of 

 distribution of families in the second volume of his great work 

 shows that but one genus of these reptiles enters his 

 Canadian sub-region. This is Gerrkonotus, placed by Mr. Boulenger 

 in the latest British Museum Catalogue in the Family Anguidae. On 

 looking through that Catalogue I find, on the other hand, that the 

 Sonoran Region is characterised by no fewer than 22 genera of lizards : 

 — Eublepharis, Anolis, ^^'Dipsosaunis, ■■'■Saiiroiualus, '■'■'■ Crotaphytus, ''Petro- 

 saunis, '■■'■Callisauriis, '■Uma, ■■'Holbrookia, Uta, Sceloponis, Phvynosoma, 

 Gerrkonotus, Ophisanrus, ''Anniella (forming a peculiar family), Heloderma, 

 '■'Xantusia, '^'Cnemid op horns, Chirotes, "^'Rhineiiva, Lygosoma, and Eumeces, 

 of which the 1 1 marked with an asterisk are not found elsewhere. 

 The genera which are not peculiar have either Neotropical affinities 

 or are represented in corresponding latitudes in the Old World. The 

 Tortoises tell the same story. A survey of the land and fresh-water 

 genera of Chelonians, as given in Mr. Boulenger's British Museum 

 Catalogue, shows that only two genera, Tvionyx and Emys, neither 

 peculiar to America, reach the Boreal " district, while the Sonoran, in 

 addition to these, possesses Chelydra, Macvoclemmys, Cinosternnm, 

 Chrysemmys, '■•'-Malcicoclennnys, Clemmys, '•'Cistndo, and Testudo, the two 

 distinguished by the asterisk being peculiar. The Sonoran Region 

 is further to be distinguished by the genus Alligator, among the 

 Crocodiles. 



" The former, indeed, seems not to pass Dr. Merriam's transition zone. 



