INTRODUCTION. 
Tue latest general work on Frogs—‘ Catalogue of the Batrachia 
Salientia in the British Museum,’ published in 1858—contains the 
descriptions of 283 species. The present volume contains the de- 
scriptions of 800 species, more than two thirds of which have been 
seen by the author. é 
In 1858 the Collection of Tailless Batrachians in the British 
Museum contained 214 species, represented by 1691 specimens. 
Ten years later the number of species had increased to 313*. The 
two numbers amount now to 522 and 4692 respectively. 
The classification adopted here is derived from that proposed by 
Mr. E. D. Cope; but it has been modified in many respects. It 
appears to the author undeniable that the principles of classification 
laid down by Mr. Cope are more in accordance with the natural 
affinities of the genera of Tailless Batrachians than those employed 
by other authors; this is amply proved by all we know of their 
geographical distribution, development, and physiology. 
An objection has been made to the adoption of this system, but on 
a rather trivial ground. It is the supposed difficulty of ascertaining 
osteological characters ; and quite recently Dr. P. Brocchi + questions 
whether it is possible to apply in descriptive zoology a classification 
that requires the sacrifice of one or several of the specimens. But, 
* Cf. Ginther, P. ZS. 1868, p. 478. 
+ Mission Scientif. au Mexique, Batraciens. 
