IV PREFACE. 



being a natural one. Having defined these snakes as 

 ' Colubrinse without grooved or perforated teeth in front,' 

 we are obliged to abandon the principle of dentition for 

 further subdivision, there being no other natural character 

 which corresponds to its variations ; therefore I consider 

 the principles introduced by Boie and Schlegel to be the 

 best upon which to base a natural arrangement, and I 

 have foDowed the system laid down in the Essai. One 

 great merit of the Erpetologie generate I well know how 

 to appreciate :— The characters of the dentition offer in 

 a great many cases a decisive method for distinguishing 

 the species ; but as regards the combination of the species 

 into genera and families, it is of no greater importance 

 than any other external character by itself. But still I 

 am always glad to use the dentition as one of the cha- 

 racters of genera or families wherever that is possible, 

 namely wherever it corresponds with the mode of life, 

 the general habits and the 'physiognomy.' Schlegel's 

 two large genera, Coluber and Herpetodryas, include such 

 a number of intermediate forms, that, for want of other 

 means of dividing them into smaller groups, I have em- 

 ployed the principle of dentition ; but I am far from 

 being satisfied with it, except in the one genus Zamenis, 

 which is otherwise well defined even by its geographical 

 distribution. I am perfectly aware that the characters of 

 my families (Schlegel's genera) are not of absolute value ; 

 but where nature has not created distinctly separated 



