vi PREFACE. 



well-known and very common circumstance with regard to several groups of 

 animals. In our present researches there exists a remarkable example of this 

 fact in the genus Proctotretus, consisting, as is now known, of at least fourteen 

 species, all inhabiting the western coast of South America. These facts, 

 interesting as they are, have never been sufficiently investigated, although, it 

 must be confessed, there are so many anomalies in relation to this subject, that 

 we must despair of ever reducing the facts in question to any thing like fixed 

 laws. 



The close approximation of the Raniform and Hyliform groups of the 

 Anourous Amphibia is strikingly illustrated by several new forms obtained by 

 Mr. Darwin, which are so perfectly osculant between the two families, that it is 

 difficult to assign them a decided location. And the addition of some bufonine 

 forms in the family Ranidce, as at present constituted, and on the other hand of 

 some amongst the Bufonidce, which are no less raniform in their general structure 

 and habits, render it increasingly probable that the single character of the 

 presence or absence of superior maxillary teeth, must be considered as in- 

 sufficient to constitute alone a natural distinctive family character. There are 

 several minor points bearing upon the natural arrangement of the Anourous 

 Amphibians, which are illustrated by the characters of some of the species 

 now first described, which will doubtless at some future time assist in the 

 construction of a classification of these animals, bearing at least a nearer 

 approximation to their natural arrangement than any that has hitherto been 

 promulgated. 



The Ophidians have been placed in the hands of Mons. Bibron, who is 

 at the present time engaged in completing his admirable history of Reptiles, 

 by the publication of those volumes which are devoted to this order; and 

 it must be considered a fortunate circumstance that the delay which has 

 taken place in the appearance of that portion of his labours, has thus afforded the 

 opportunity of embodying in so perfect a work, the numerous discoveries of 

 Mr. Darwin in this particular department of Erpetology. 



T. B. 



Hornsey, Sept. 2, 1843. 



