PREFACE. V 



families, the systematist must not establish them. I 

 think that neither in the families nor in the genera here 

 adopted, are there such heterogeneous forms comprised, 

 as in the 8th, 10th, 11th and 12th families of the ' Ser- 

 pens non venimeux' of Dumeril, and in the 2nd, 3rd, 5th 

 and 6th of his ' Opisthoglyphes ;' nor are the most allied 

 forms so widely separated, as we often find to be the case 

 in the same parts of that work. 



" The chief object of every branch of Zoology I consider 

 to be the discerning of species, and I object to the ten- 

 dency of those zoologists who establish a new species for 

 almost every individual, and so destroy the entire basis 

 of our science. In comprising sometimes many varieties 

 under one species, I have no fear of going too far, as I 

 think it preferable to characterize as a variety a form, 

 which may afterwards prove a real species, rather than 

 overburden science with nominal species. The number 

 of specimens of Colubrine Snakes in the British Museum 

 Collection (3100) has afforded me ample means for di- 

 stinguishing the species ; and I have again convinced my- 

 self, that it is easier to characterize a peculiar form as a 

 new species, than to recognize it as a variety. 



" In accordance with the plan adopted by Dr. Gray, 

 I have prefaced each diagnosis with the synonymy of 

 the species, — a task which would have been the most 

 tiresome part of the work, but for Dr. Gray's kindness 

 in giving me the free use of his own MSS. I have found 



