SAND LIZARD. 19 



no reference whatever to the peculiarity of habit which forms 

 the legitimate foundation for the generic distinction. This 

 will be found to be the case, for instance, in some of the 

 genera of saurian reptiles, and even in the generic distinction 

 of our only two native species ; the genus Zootoca, to which 

 our common Lizard belongs, being characterized, as regards 

 habit, by the circumstance that the species of which it is 

 composed are ovo-viviparous. This is a character to which 

 the structure of any of its external organs bears no possible 

 relation ; but as it is found that the species having this habit 

 is externally characterized by some peculiarity in the form 

 and situation of certain little scales about the head, having, 

 however, no possible reference to the habit in question, such 

 peculiarities are employed as convenient and permanent cha- 

 racters by which it may be distinguished. 



It must, however, be acknowledged that there are cases 

 in which a numerous group is found to consist of several 

 divisions, each of them distinguished by some point of form 

 or structure, the use or object of which is absolutely un- 

 known or unintelligible to us, and in which the habits, as far 

 as we know them, are not conspicuously different. For the 

 sake of convenience in some cases, and of consistency and 

 harmony of system in others, these groups may, notwithstand- 

 ing this uncertainty, receive with propriety a distinctive ge- 

 neric appellation ; but, wherever it is possible, generic groups 

 ought only to be formed where Nature has herself pointed 

 out their distinction. 



The generic and specific characters of the Lacertine group 

 have only of late years received the degree of attention which 

 they deserved. The divisions and subdivisions of this nu- 

 merous family had been either overlooked, or so arbitrarily 

 defined as to be detected with difficulty, and their value 

 had been greatly misunderstood. The employment of mi- 

 nute characters in the structure and proportions of the differ- 



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