192 BULLETIN 114, UNITED STATES NATIONAL MUSEUM. 



frontal plates and overlaps the anterior edge of the frontal. An- 

 terior to this the snout is light; mottled with dark, except for a narrow 

 bar of black across the prefrontal-internasal suture. There are 

 usually two oval light spots near the parietal suture; a black band 

 extends diagonally from the eye to the angle of the mouth. The 

 labials and chin shields are whitish, except for more or less black 

 near the sutures. 



The dentition, as indicated by a dozen specimens from all parte 

 of the range, is as follows: Maxillaries, more often 12, less often 13, 

 larger in front, decreasing behind, except that the last two are some- 

 what longer and stouter than any of the preceding; mandibulars, 

 11 to 15, most often 13, distinctly larger anteriorly, decreasing rapidly 

 behind, the third, fourth, and fifth largest, a slightly greater space 

 between the fourth and fifth or between the fifth and sixth; palatines, 

 9, 10, or 11, decreasing slightly in size posteriorly; pterygoids, 17 

 to 23, becoming smaller posteriorly. 



Although sufficiently distinct as a rule, there is no characteristic 

 which will always distinguish triangulum from syspila. These two 

 forms have been contrasted under the description of the latter. 

 Specimens of doubtful identity will be found near the common 

 boundary of their ranges, and in Virginia, Maryland, eastern Penn- 

 sylvania, New Jersey, Delaware, and perhaps in West Virginia. 

 Typical tnangulum occurs in all these states, but many individuals 

 show marked degeneracy in pattern and in scutellation. Specimens 

 will be found with as few as 28 dorsal saddles, which extend to the 

 second or first row of scales, and with head markings typical of 

 syspila, but such individuals average to have a less number of ven- 

 trals and caudals, and a lower scale formula than similar exam- 

 ples of syspila. Specimens from these localities identifiable in the 

 key as syspila must, for the present at least, be referred on geo- 

 graphic grounds to triangulum. ^ 



Habitat and Jiahits. — From Wisconsin and Illinois, east to New 

 England, this is a common and well-known snake, but in the south- 

 eastern States, except in the mountains, it appears to be rare. It is of 

 very general occurrence in all upland situations, woods and fields, and 

 is not uncommon in the vicinity of dwellings and stables. It does 

 not appear to haunt the shores of streams or lakes, but may be 

 expected in most other situations. Its wide choice of habitat is 

 related to the v/idespread occurrence of its principal food — mice. 

 For the vicinity of Saginaw Bay, Michigan, Ruthven (1911, 267) 

 says that '' they were mostly found in the deca3dng logs on the fossil 

 beaches and pine ridges, where they fed, in part at least, on the 

 Michigan mouse iPeromyscus maniculatus hairdii) and the blue- tailed 

 sldnk (Eumeces quinquelineatus) , as remains of these auimals were 

 found in the stomachs examined." A specimen taken in a hay field 



