iv PREFACE. 



genera, where the characters seemed sufficient. As yet we know 

 little (except of the borders) of Africa, Australia, andTropieal America, 

 and there are but few collectors who have directed particular 

 attention to this class of animals. Thus we may not only affirm 

 Avith some certainty that many families at present poor in species 

 will soon be enriched, but we may even venture to prognosticate that 

 at least some of the missing forms, which I have pointed out, will 

 be discovered. The progress made in our knoAvledge of the Batrachia 

 Ayiura during the last fifty years may be seen at once by the following 

 comparison of the number of species given by different authors : — 



Shaw in 1802 51 species. 



Tschudi in 1838 110 species. 



Dume'ril & Bibron (vol. ix.) in 1854 . . 164 species. 



The present Catalog-uc in 1858 280 species. 



" There are, besides, many species which I could not introduce into 

 this Catalogue, on account of the imperfect descriptions given of their 

 systematic characters. 



''■ Dr. J. E. Gray has collected in his MSS. (the free use of which, 

 with his usual kindness, he has permitted me) diagnoses of many 

 species from papere scattered through various journals, and so directed 

 my attention to species which I might otherwise have overlooked. 

 He proposed to arrange these animals into two groups, according to 

 the form of the diapophysis of the sacral vertebra. I fully acknow- 



