18 LACERTID.E. 



Lacerta agilis, Linn. Fn. Suec. 284. — Ib. cura Retz. 289. — Syst. Nat. I. 



363, n. 15. Mull. Zool. Dan. Prod. p. 36, n. 299. 

 Merr. Syst. Amph. p. 66, sp. 13. C. L. Bonap. Faun. 

 Ital. cum Icon. 

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

 Sc. Nat. XVI. p. 376, sp. 3, t. Ixxvi. f. I. 2. Jenyns, 

 Brit. Vert. p. 291. 

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

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

 Lezard 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 diLinneo, 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 significa- 

 tion, and the characters themselves of slight value and im- 

 portance, 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 professes 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 ob- 

 vious or probable moment in any of the habits of life, — as, 

 for example, the degree of developement of the thumb in 

 some genera of monkeys, or the modification of the carnivo- 

 rous propensity in allied groups of carnivora, evidenced 

 by the greater or less degree of acuteness in the tuber- 

 cles 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 conve- 

 nient, or the only tangible characters of the group may have 



