VARIATIONS OF GARTEIl-SNAKES. 107 



from any other form in the Radix groiij), l)()tli owing to the somewhat 

 greater length of tail in megalo'ps and to the shorter tail in proximus 

 in northern ^lexico. Since the scutellation is practically the same in 

 the two forms, except that the dorsal scale formula in proximus is 

 slightly smaller, it may be that proximus is a direct relative of 

 megalops which has pushed eastward into the eastern coastal-plain 

 region of northern Mexico, and from here southward and northward 

 into the regions which it now occupies. However, it is quite distinct 

 from megalops at the present time, in the long tail and more slender 

 bod}^, and it is to the northward that we must look for its closest 



relatives. 



SACKENI.a 



Description. — This beautiful snake has received but little atten- 

 tion from herpetologists and is represented in collections by but few 

 specimens. The scutellation may be defined as follows: Dorsal 

 scale rows, 19-17; supralabials, 8; infralabials, 10^ ventral plates, 

 154-171; subcaudal scutes, 109-134; tail length, .32-.38. The col- 

 oration is similar to light specimens of proximus, the lateral stripe 

 being on the third and fourth rows (yellowish or greenish), the 

 ground color usually a shade of brownish olive, and the belly and 

 labials light and generally unmarked. As in proximus, the ventral 

 spots are usually absent, but not always, and the lateral spots are 

 generally fused irregularly, although occasionally distinct in the 

 usual two rows between the stripes; even when distinct on the skin, 

 however, they are not represented on the scales except by a narrow 

 black border along the dorsal, and occasionally the lateral stripes. 

 The lateral stripe is always distinct, but the dorsal is generally 

 obscure and often entirely wanting; when present, it covers all or 

 nearly all of the median three rows. 



Ilahits ami hahitat relations. — Saclceni is a very interesting snake. 

 In the length of tail and slender body it represents the extreme in 

 the group and genus, and with the attenuated form is coupled an 

 agility of movement that we doubt is exceeded in any other garter- 

 snake. While comparatively little is written upon its habits, there 

 is slight doubt but that, like proximus, sackeni is quite aquatic in 

 its habits. Thus, Ditmars (1907, 219-220) writes, "In habits this 

 species is very similar to the ribbon snake [sauritus]. It is very 

 aquatic, and is seen frequently sunning on the branches of bushes 

 that overhang the water, into which it drops when alarmed." Loenn- 

 berg (1894, 329) remarks of the specimens obtained by him in Florida, 

 "All were caught in the grass in wet places." Personally I have 

 been able to make few observations on the habits of this form. During 

 the summer of 1905 I reared, two broods which were born on July 

 19. The young resembled those of other forms in habits except for 



o Thamnophis sauritus sackeni (K'ennicott) , Proc. Acad. Nat.Sci. Phila., 1859, p. 98. 



