376 



The second genus, which may be almost called a cosmopolitan, is Co- 

 ronella, being spread over the whole globe except the Indian region, 

 where it is replaced by such modifications of the characters as to 

 justify the separation of them into new genera — Simotes and Ablabes, 

 sp. The latter, closely allied to Coronella, accompanies this genus, 

 extending over all the regions, except over the Australian one. Thus, 

 if I speak hereafter of cosmopolitan genera of Snakes, they are to 

 be understood with the restrictions mentioned. The families of 

 Snakes in the different systems are at present founded upon such 

 general characters, that in most of them genera of some or of all 

 the geographical regions are comprised ; perhaps at some later period 

 they will be limited to more contracted boundaries of less general 

 characters, thus approaching more to the borders of the geographical 

 regions. But for the present we cannot derive from them our de- 

 ductions as to the primary creation of the natural regions of the 

 earth's surface, as the ornithologist does ; and we are obliged to con- 

 fine our views to the genera : we have not even such families of 

 Snakes as are peculiar to one of the two great geographical divi- 

 sions, either to the old world or to the new, except those in which 

 the characters of the family are identical with those of the single 

 genus. This discrepancy between Ornithology and Herpetology may 

 be caused by a different systematic treatment of the characters, and 

 may be more reconciled together by time ; but there will always re- 

 main forms common to the new and old world. Therefore it is not 

 possible to give a list of Families Neogeance and Familice Palceo- 

 yeance (cf. Sclater, I.e. p. 133). 



But I may here give an account of such genera as, I think, will 

 still long remain examples of forms common to the new and old 

 world (cosmopolitan genera excepted) : they are Rhabdosoma, Co- 

 luber, Spilotes, Coryphodon, Cyclophis, Philodryas, Dipsas. I could 

 add as many other genera ; but I think such genera as Rhinostomu, 

 Dryophis, &c. will be subdivided hereafter into two. Further, with 

 regard to the aforesaid genera, the same observation as in Ornitho- 

 logy cannot be made, viz. that these are invariably genera belonging 

 to temperate regions, disappearing entirely before we reach Tropical 

 and Southern America. A part of the members of these genera 

 are peculiar to Neotropical (Tropical America) Ophidio-fauna ; a part 

 reaches the Tropics in the old world, and a third part belongs to the 

 temperate portions of both hemispheres. 



Taking the amount of similarity or dissimilarity of ornithic life as 

 a guide, Mr. Sclater states the following primary divisions of the 

 earth's surface : — 



I. Palcearctic Region (Regio Palaearctica). 



Extent. — Africa, north of the Atlas; Europe; Asia Minor; 

 Persia and Asia generally, north of the Himalaya Range, upper part 

 of the Himalaya Range (?); Northern China, Japan, and the Aleutian 

 Islands. Approximate area of 1-1,000,000 square miles. 



