67 



Batrachia. 



Amhlystoma. 

 Spelerpes. 

 Spea. 

 Rana. 



Of fishes, the common genera of the fresh waters are few. They are 

 Giyardinus, Gamhusia, HaplocMlus, and Fundulus of Cyprinodontidae, 

 and Atractosteus of the bony gars. The southward distribution of the 

 above genera terminates at various points ; but those which belong to 

 the Austroriparian region, as distinguished from the Sonoran, are mainly 

 confined to the Mexican plateau. The presence of these, together with 

 a number of peculiar forms, indicates another region of the Nearctic, 

 which is in many respects allied to the Austroriparian. This subject 

 will be considered in a subsequent paper. 



In comparing the Nearctic realm with the West Indian region of the 

 Neotropical, much less resemblance can be detected, especially in the 

 Eeptiles and Batrachia. The only identical species is the AnoUs prin- 

 cipalis, which is common to the Austroriparian region and Cuba, and 

 there are three others of West Indian origin found in the southern part of 

 riorida. The Anolis is the only reptilian genus of wide distribution in 

 the Nearctic realm which occurs in the West Indian region. The West 

 Indian genus Dromicus is represented by one species, a rare snake from 

 the coast of North Carolina. In Batrachia, there is no community of 

 species and none of genera, excepting in the case of the cosmopolitan 



genera Bufo and Hyla. 



« 



IV. — THE REaiONS. 



We may now consider the variations exhibited bj'^ the component 

 parts of the Nearctic fauna. The distribution of types indicates six 

 principal subdivisions, which have been called the Austroriparian^ 

 Eastern, Central, Pacific, Sonoran, and Lower Californian. The Austro- 

 riparian region extends northward from the Gulf of Mexico to the 

 isothermal of 77° F. It commences near Norfolk, Ya., and occupies a 

 belt along the coast, extending inland in North Carolina. It passes 

 south of the Georgia Mountains, and to the northwestward up the Mis- 

 sissippi Valley to the southern part of Illinois. West of the Missis- 

 sippi, the boundary extends south along the southern boundary of the 

 high lands of Texas, reaching the Gulf at the mouth of the Eio Grande. 



