VARIATIONS OF GARTER-SNAKES. 181 



Indiana; Oberlin, Columbus, Sandusky, Montgomerv County, Yellow 

 Creek, Ohio; Washtenaw County, Grand Rapids, Grosse Isle, Living- 

 ston County, Eaton County, Oakland County, Oceania County, 

 Crawford County, Iosco County, Alma, Isle Royale, Porcupine Moun- 

 tains, Bessemer, Houghton County, Baraga County, Marquette, Mich- 

 igan; Thompson's Lake, Racine, Lauderdale, Milton, Wisconsin; 

 Lucknow, London, Wellington County, Gravenhurst, Ontario, 

 Canada. 



It occurs on the nearest of the outlying islands in the Atlantic Ocean 

 and Gulf of Mexico. The most northern reliable records are Isle 

 Royale, Michigan, and Gaspe, Quebec (Cox, 1899), but it doubtless 

 ranges somewhat beyond tliis latitude. On the other hand, its 

 western hmits are neither well laiown nor definitely ascertainable, 

 for in tliis direction it intergrades with parietalis, the ranges of the 

 two forms being apparently conterminous. At present its western 

 boundary may be considered as closely approximating that of the 

 hard-wood forest. Without doubt typical specimens will be found 

 to occur in Minnesota and Iowa, but this can not now be settled, inas- 

 much as the principal character (red interspaces between the lateral 

 spots) that distinguishes parietalis from sirtalis disappears rapidly in 

 preserved material. 



Variation. — Notwithstanding the wide range of sirtalis, the variation 

 in scutellation is slight. As already stated, the dorsal scale formula is 

 so constantly 19-17 that but two specimens out of some six hundred 

 examined have any other. In these two specimens (one each from 

 Fort Bassenger, No. 22696, and Georgiana, Florida, No. 14833, in 

 the U. S. National Museum) the formula is 19-21-19-17. The 

 labials are comparatively nearly as constant, the average formula 

 for localities throughout the range being very close to 7/10. Occa- 

 sionally specimens, regardless of their geographic position, exhibit 

 8 supralabials, and much more rarely 6, while contrary to this the 

 variation in the infralabials 8, 9, or 11 apparently tend somewhat 

 more strongly toward a lower number than 10. This is illustrated 

 in the diagrams (figs. 79-80), which illustrate the conditions in 113 

 specimens from southeastern JVIichigan (Livingston, Washtenaw, 

 Oakland, Eaton counties), and the variations in the material examined 

 from every other locality is apparently very similar. 



The number of ventral plates varies from 137 to 167, and the 

 average is rather constant throughout the range. I believe, how- 

 ever, that there is a slight reduction in the mean number m speci- 

 mens from extreme eastern United States. Thus, the diagram 

 (fig. 81) shows that the average for specimens west of the Allegheny 

 Mountains is very close to 154 (between 150-155), but in specimens 

 from Maryland, Massachusetts, and Rhode Island the mean is be- 

 tween 145-149. Based as they are on rather extensive series, I 

 33553— Bull. 61—08 13 



