67 

 Bateachia. 



Amblystoma. 

 Spelerpes. 

 Spea. 

 Rana. 



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

 Oimrdinns, Oamhusia, Haplochilus, and Fundulus of Cyprinodontidae, 

 and Atraciosteiis 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. 



lu 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- 



i c'(j)«/is, which is common to the Austroriparian region and Cuba, and 



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



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



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



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



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



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



jenera Bvfo and Hyla. 



IV. — THE REGIONf^. 



We may now consider the variations exhibited by the component 



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



pncipal subdivisions, which have been called the Austroriparian, 



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



pparian region extends northward from the Gulf of Mexico to the 



Sothermal of 77° F. It commences near Norfolk, Va., and occupies a 



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



)uth of the Georgia Mountains, and to the northwestward up the jMIs- 



[ssippi Valley to the southern part of Illinois. West of the Missis- 



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



gh lauds of Texas, reaching the Gulf at the mouth of the Ilio Grande. 



