SAND LIZARD. 19 



Lacerta stirpium, Daud. Rept. III. p. 155, t. xxxv. f. 2. Duges in An. des 



Sc. Nat. XVI. p. 376, sp. 3, t. lxxvi. f. 1, 2. Jenvns, 

 Brit. Vert. p. 291. 

 „ arenicola, Daud. 1. c. p. 230, t. xxxviii. f. 2. 

 „ anguiformis, Sheppard, in Linn. Trans. XVI. p. 51. 

 Lizard des Souches, Daud. 1. c. M. Edw. in An. des Sc. Nat. XVI. p. 65. 83. 



t. v. f. 4, et t. viii. f. 1.2. 

 Lacerta di Lintico, C. L. Bonap. 1. c. 



Because it may appear to many persons not accustomed 

 to the use of what are commonly termed essential generic 

 or specific characters, that many of those phrases by which 

 such characters are expressed are confined in their signifi- 

 cation, and the characters themselves of slight value and 

 importance, it may not, perhaps, be useless, before we 

 proceed to describe the species, to offer a few words 

 explanatory of their employment, especially with reference 

 to those groups of animals on which the present work pro- 

 fesses to treat. It has always appeared to me that generic 

 distinctions should, as far as possible, be limited to such 

 differences of structure as indicate a difference in the habits 

 of the animals. Thus, the absence in one species, and the 

 presence in another, of an organ or part of an organ, the 

 application of which is of obvious or probable moment in 

 any of the habits of life, — as, for example, the degree of 

 development of the thumb in some genera of monkeys, or 

 the modification of the carnivorous propensity in allied 

 groups of carnivora^ evidenced by the greater or less degree 

 of acuteness in the tubercles of certain teeth, — will form 

 good grounds for such a distinction. Now it is evident 

 here that what is called the generic character is merely 

 the phrase expressive of some point of structure belonging 

 to the whole group in which a certain habit obtains. In 

 many cases even, the most convenient, or the only tangible 

 characters of the group may have no reference whatever to 



the peculiarity of habit which forms the legitimate founda- 



c 2 



