108 



GliOGRAl'iilCAL DlcXKIBUXION 



Thua we have 9 genera and 34 species peculiar to the European, 

 and 8 genera and 20 species to the Asiatic Subregion ; whilst 5 

 genera and 7 species are spread over both. 



It is also interesting to observe the gradual transition of the 

 European Caudata into the North -American fauna, as is shown in 

 the following table : — 



Number of Species in the 

 European Asiatic N.-American 

 Subregion. Subregion. Region. 



Salaniandrinse 20 4 2 



Amblystomatinte . . 8 17 



Amphiumidse . . 1 3 



whilst, on the other hand, we must notice the presence of Pelo- 

 batidce in Europe and North America, they being absent in the inter- 

 mediate Asiatic Subregion ; also the presence in Europe of a species 

 of Spelerpes, a genus abundantly represented in North America and 

 not in Asia ; and, finally, the affinity which exists between the 

 European Proteus and the North-American Necturus. 



No species is known to be common to the Europo-Asiatic and 

 North-American Eegions, but some, such as Rana temporaries Bufo 

 calamita, &c, and their North-American representatives, are ex- 

 tremely closely related, and to be distinguished with difficulty only. 



If we except the very widely distributed genera Rana, Bufo, and 

 Hyla, we have only two genera which are common to both regions, 

 viz. Molge and Spelerpes. 



2. The North-American Region. 



It is difficult to draw a boundary line between the North- American 

 and the Tropical- American Regions ; a large territory, extending 

 from the Rio Grande del Norte to the Isthmus of Tehuantepec, has 

 a North-American fauna in its elevated parts, whilst a tropical 

 flourishes in its low country ; besides, as in all intermediate districts, 

 a gradual mixing of the two faunas obtains. We adopt the boundary- 

 line drawn by Wallace. 



The North -American Region is particularly characterized by the 

 great abundance of Caudata, viz. 55 species (that is, more than half 

 of those actually known) occurring within its boundary. It has one 

 family peculiar to it, the Sirenidce. The Salamandroid subfamilies 

 Desmognathince and Pleifiodontinm are also characteristic of this 

 region, although the latter has one representative occurring in Europe 

 and a few in the Tropical-American Region. The family Ampld- 

 umidce may also be considered characteristic of the North-American 

 Region, as it possesses three out of four species and two out of three 

 genera. The Ecaudata are chiefly Rana and Hylidce : of Bufo there 

 are relatively few species ; the Pelobatidce are represented by the 

 genus iScaphiopus. In the South two outposts occur from the 

 Tropical-American Region, viz. Engystoma and Hylodes, both repre- 

 sented by a single species. 



