The common garter snake ( Thamnophis sirtalis ) has by far the most extensive geographic range of any North American reptile, covering most of the continental United States from the Atlantic to the Pacific and from south of the Mexican boundary far north into Canada and southeastern Alaska. Of the several recognized subspecies, the eastern T. s. sirtalis has the most extensive range, but that of T. s. parietalis in the region between the Mississippi River and the Rocky Mountains is almost as lar

Thamnophis sirtalis parietalis Say was described (as Coluber parietalis ) in 1823 from a specimen obtained in what is now Washington County, Nebraska, on the west side of the Missouri River three miles upstream from the mouth of Boyer's River [Iowa], or approximately eight miles north of Omaha. Although the type locality was unequivocally stated in the original description, Nebraska was not mentioned since the state was not yet in existence. Because the mouth of Boyer's River, the landmark by me

Wherever it occurs at all, the common garter snake is usually abundant. Because of its diurnal habits and the concentration of its populations along watercourses, it is not likely to be overlooked. There are few, if any, remaining large areas in the United States where herpetologists have not carried on field work. It may be anticipated that certain rare and secretive species will still be found far from any known stations of occurrence, and seeming gaps in the ranges of these species will event

Most specimens of a population of sirtalis occurring in New Mexico are recognizably different from most specimens of other populations. This New Mexican population is therefore here recognized as a distinct subspecies: Thamnophis sirtalis ornata Baird Eutaenia ornata Baird , 1859:16. Eutaenia sirtalis dorsalis Cope , 1900:1076. Thamnophis sirtalis parietalis (part) Van Denburgh , 1924:222. Type. —U. S. Nat. Mus. No. 960, obtained at El Paso, Texas, at some time in the eighteen fifties by Col. J.

From most of the vast area occupied by parietalis , material has not been available to us, and our concept of this subspecies is based chiefly on specimens and living material from Kansas and northeastern Colorado. A total of 520 live parietalis has been examined from the University of Kansas Natural History Reservation some 130 miles south and a little east of the type locality in Nebraska. These probably differ but little from typical specimens. The range of individual variation in pattern is

Like most widely ranging subspecies, parietalis and fitchi vary geographically and local populations often are noticeably different from typical material. It is possible that future revisors will recognize additional subspecies, but in the variant populations known to us the degree of differentiation is slight as compared, for instance, with that in the subspecies of Thamnophis elegans . Scalation is remarkably uniform in all the subspecies of sirtalis , but coastal and northern populations tend

Of many specimens examined from eastern Oregon, Idaho, Utah, Wyoming and Colorado, few were typical of either parietalis or fitchi . Many were intermediate in some respects or showed a composite of characters of the two subspecies. No well-defined belt of intergradation exists, but the transition extends over more than a thousand miles, with local populations somewhat isolated and slightly differentiated along divergent lines. In view of this situation some plausibility could be claimed for any

Dr. Doris M. Cochran of the United States National Museum kindly furnished information concerning the type specimen of Eutainia dorsalis formerly in the National Museum collection but now lost. Dr. James S. Findley of the University of New Mexico and Dr. Ralph J. Raitt of New Mexico State University contributed habitat notes and records of specimens and loaned us critical specimens of T. sirtalis from New Mexico. Drs. George F. Baxter of the University of Wyoming, John M. Legler of the Universit

Baird, S. F. 1859. Reptiles of the boundary. United States and Mexican Bound. Surv., 2, 1-35, 41 pls. Baird, S. F. , and Girard, C. 1853. Catalogue of North American reptiles in the Museum of the Smithsonian Institution. Smithson. Miscl. Col., part 1, Serpents., pp. xvi + 172. Brown, B. C. 1950. An annotated check list of the reptiles and amphibians of Texas. Baylor Univ. Studies, pp. xii + 259. Bundy, R. E. 1951. New locality records of reptiles in New Mexico. Copeia, 1951 (4):314. Cockerell, T