316 Zoological Society : — 



better, anatomical characters ? As the palaeontologist endeavours to 

 show what organic forms reappear in a stratum above or below an- 

 other, and where a new creation begins, so must the zoologist do in 

 the horizontal distribution of animals on the earth's surface. Our 

 Rana esculenta is represented by Rana halecina : specimens of the 

 former exhibit sometimes quite the same coloration as that con- 

 stantly found in R. halecina ; but they invariably differ in the struc- 

 ture of the vocal organs. Bufo vulgaris of the Old World is repre- 

 sented in North America by B. le^itiginosus, in South America by 

 B. chilensis — all sufficiently distinguished by the structure of the 

 skull. Hgla arhorea has its representative in JET. ewphorhiacea from 

 the table-land of Central America. Thus we find one of our most 

 common Anura to be the same in the New "World, and three others 

 represented by closely allied species. Our fifth common species, 

 Bombinator igneusy is a more local species, and has no representative 

 in North America. No species of the TJrodela is common to both 

 regions, not even a genus ; but in both we have not only such 

 genera as are assigned by their structure either to living in water or 

 on land, but also those intermediate forms which cannot properly 

 be brought under either category. Among the TJrodela with free 

 gills or gill-openings, Sieboldia exhibits at least such similarities 

 with Menopomay and Proteus such with MenobranchuSy that they 

 may well be considered as representing each other in the two re- 

 gions. Thus we find the Nearctic and Palsearctic regions nearer 

 allied, in respect to their Batrachio -fauna, than they are to any other. 

 Cystignathus and Engystoma each exhibit one species in the 

 southern parts of North America, these genera belonging, in fact, 

 to the Tropics. 



VI. Neotropic Region. 



Characteristic forms. — Pipay Pseudis, CalyptocephaluSy Cyclo- 

 rhamphusy PithecopsiSy LimnochariSy Hylorhinay PyxicephaluSy 

 CeratophrySy LeiuperuSy Pleurodemay AlsodeSy PhryniscuSy Bracky- 

 cephalus, Rhinodermay AtelopuSy Engystomay Otilophus, Elosia, 

 CrossodactyluSy PhyllobateSy HylodeSy Nototremay OpisthodelphySy 

 TrachycephaluSy Phyllomedusay Hylaplesiay Rhinophrynus. 



Form common to other regions. — Cystignathus. 



On the northern boundary of this region the Batrachio-fauna is 

 mixed with Arctic forms, which is also the case as regards other mem- 

 bers of the animal kingdom, without taking into account those animals 

 which, living on mountains, find by this vertical elevation the con- 

 dition of a more northern climate. The absence of the genus Rana 

 may be pointed out as a character of this region ; one species, how- 

 ever, which I think I have recognized as R. Lecontii of Girard, 

 reaches, together with Hyla versicolory into the South of Mexico, and 

 is found in localities with Bufo granulosuSy Hylaplesiay and Rhino- 

 phrynus. Bufo chilensis ranges along the western coasts to Califor- 

 nia. But putting aside these examples, we meet, on entering Mexico, 

 that Batrachio-fauna by the abundance and peculiarity of which this 

 region is widely distinguished beyond all the others. There we 

 find the greatest number of species of Bufo and Hylay and those 



