Dr. A. Giinthcr on the Geogy^aphical Distribution of Reptiles. 233 



V. Nearctic or North American Region (Regio Nearctica). 



Characteristic forms. — Charina, TFeitona, Conopsis, Conocephalus, 

 Cmyhophis, Osceola, Ninia, Lodia, Sonora, llhinochiluSy Tantillay 

 Slmotes ? coccineus, Ischnognathus, HelicopSy Farancia, DimadeSy 

 Abastor, Virginia, Contia, Pituophis, Cenchris, Crotalophorus, 

 UropsophuSy Crotalus. 



Forms common to other regions. — Heterodon, Coluber y Cory' 

 pthodon, HerpetodryaSy CyclophiSy Elaps. 



. There is some difficulty in stating the southern boundary of this 

 region ; the Tropical fauna advances along the Isthmus of Panama, 

 and, extending over the again expanding part of Southern Mexico, it 

 is gradually mixed with the Arctic fauna. And in these parts the 

 fauna of the same latitude is the more mixed on account of the great 

 diiferences of the elevation above the level of the sea, and the result- 

 ing great variety of climate in a small space ; but as the climate gra- 

 dually assumes the tropical character, so also do vegetative and 

 animal life. Nevertheless we have in the New World two entirely 

 different creations, radiating from the system of the Mississippi in the 

 north, and from that of the Amazon in the south ; and in each of 

 those smaller provinces situated on the boundary between both regions, 

 it will be a question whether the larger number of its species belong 

 to northern or southern forms. As far as we are able at pre- 

 sent to judge, the tropic of Cancer may be considered as the bound- 

 ary. No Snake is to be found north of 60° N. lat., — a latitude 

 where in the Palsearctic region Pelias berus exists. But taking 

 6,500,000 square miles as the amount of the whole dry land in this 

 region, and allowing seventy-five* species as peculiar to it, we have 

 one species to every 87,000 square miles, or four species to the same 

 area for which we found only one in the Palaearctic region. Thus 

 this region indicates a much greater degree of intensity of species 

 than the Palsearctic region j but if it be stated that it also surpasses 

 the j53thiopian region, this I consider as not an established fact, but 

 only an appearance caused by the circumstance that North America 

 has been much more fully explored than Africa. Even then, if we 

 consider (according to Dr. Gray's system) Charina and Wenona to 

 be BoidcB, the ratio of this section to the number of Colubrina is very 

 small (1 : 18), the ratio between Viperina and Colubrina being large 

 (1 : 5) ; in this respect this part of the fauna quite agrees with the 

 same part of the Old "World. 



Among the non-venomous Colubrina the two families of Calama- 

 ridce and NatricidcB offer the most generic and specific forms. The 

 type of Heterodon is a North American form ; but one species is also 

 found in South America. 



* Without summing up the number of all the North American species de- 

 scribed since the publication of the * Catalogue of North American Reptiles ' by 

 Baird and Girard, 1853, I only mention that they describe therein 1 19 species. 

 What I think of such species is shown by the synonymy of the North American 

 Snakes in my Catalogue. 



