INTRODUCTION. 



The 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. 



In 1858 the Collection of Tailless Batrachians in the British 

 Museum contained 21-1: 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 natiiral 

 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 S3'stem, but on 

 a rather trivial ground. It is the supposed difficulty of ascertaining 

 ostcological characters ; and quite recently Dr. P. Brocchi t 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. Giinther, P. Z. S. 1868, p. 478. 



t Alission Scientif. au Mexique, Batraciens. 



