CROCODILIANS, LIZARDS, AND SXAKES. 1015 



Eutii'niffi are the most abundant suakes in North America and .Mex- 

 ico. Where all other species are absent, either through hostility of 

 the climate or of enemies, individuals of this genus remain. This i^er- 

 sistence may be ascribed to several causes. One of these is their great 

 fecundity. Professor Baird -mentions a specimen of E. sirtalis which 

 produced eighty young at a birth. Another cause is their readiness to 

 seek concealment in water, so that they most readily escape observation. 



Several of the sij^ecies are pugnacious in their disposition. Siich is 

 the case with the two which have the widest distribution and greatest 

 abundance of individuals, the U. sirtaUs Linnams and JE'. cleyans Baiid 

 and Girard. Their bite, it is needless to remark, is perfectly harmless. 

 Some of the species possess great elegance of form, as those of the E. 

 satirita group. Others have much brilliancy of color, as the metallic 

 green of some forms of the E. proxima and the red and black of the 

 E. sirtaUs concinna. 



The genus Enttenia presents especial attractions to the student who 

 desires an illustration of the phenomena of variation and constancy in 

 the physical characters of animals. In few genera do we And so well 

 illustrated the jjersistence of specific characters exhibited side by side 

 with variations of the same. We have here, therefore, examples of 

 the appearance or disapi)earance, as the case may be, of characters in 

 connection with or without apparent connection with the environment. 



The species of Eutcenia differ as follows: 



I. Second, and usually first, row of scales ke«^led; orbit bounded below by Two labial 

 l^lates. Lateral stripe on the third and fourth rows of scales. 



1. Temporal scales 1-2. 



* Tail equal or exceeding one-third total length ; first row of scales much 

 longer than diM>p ; strongly keeled ; scales in 19 rows. 

 Superior labials 8. longer than high; very slender; cidor metallic olive. 



A', nackenii Keunicott. 

 Superior labials 7, longer than deep; very slender; color brown. 



E. saitrita Linnaeus. 

 **Tail less than a third and more than a fourth the total length; superior 

 labials 8. 

 Head Hat; superior labials longer than high; scales in 19 rows, inferior 



row keeled, longer than deep JJ. proxima Say. 



Head elevated, superior labials higher than long; scales in 21 rows, infe- 

 rior row as deep as long /;.'. megalops Haird and Girard. 



***Tail more than one-fourtli and not less than one-Hfth the total length; 

 scales in 21 rows, the inferior row as dceji as long, and weakly or 

 not keeled. 

 Superior labials 7: tail less than 1.5 times in total length. 



h\ Kidix Raird and (Jirard. 

 Superior labials 8; tail more than 4.5 times in total length. 



K. macroatemma Kennicott. 



2. Temporal sciiles 1-1. 



Tail between one-iifth and one-fourth the total length; superior labials 7; 

 head little distinct; lateral stripe bright and black bordered, on 

 second, third, and fourth rows of scales K. hiitlerii Cope. 



Tail between one fourth and one-third the total length; superior labials 8; 

 head qu.ite distinct; lateral line faint on third and fourth rows. 



£. nttiloris Cope. 



