. Bulletin - United States National Museum. Science. VARIATIONS OF GARTER-SNAKES. 1)9 Hahits and hahitot relations.—Rarely is it possible to obtain a suf- ficient number of records to map in detail the range of any form, but if we kno\y its preferred habitat we can, in doubtful regions, determine more or less accurately the probable extent of its range by the limits of the enyironmental conditions with which it is usually associated. In the present case such data would be of great value, but unfortunately, as far as we haye been able to find, there is prac- tically nothing recorded on the habi
. Bulletin - United States National Museum. Science. VARIATIONS OF GARTER-SNAKES. 1)9 Hahits and hahitot relations.—Rarely is it possible to obtain a suf- ficient number of records to map in detail the range of any form, but if we kno\y its preferred habitat we can, in doubtful regions, determine more or less accurately the probable extent of its range by the limits of the enyironmental conditions with which it is usually associated. In the present case such data would be of great value, but unfortunately, as far as we haye been able to find, there is prac- tically nothing recorded on the habits of marcianus, mtli the excep- tion of the general conditions of the region it inhal)its. I have observed elsewhere (Ruthyen, 1907, 589) that it is occasionally at least found in the vicinity of streams, which is in harmony with the known habits of the other arid region forms in the genus (fig. 20).. Fig. 20.—Santa Cruz River at Tucson, Arizona. Thamnopuis marcianus has been found HERE. Range.—The region inhabited by /narclanns includes the Pro])hiteau region of southern Arizona, New Mexico, and Texas, the central part of the latter State, and northern Mexico, We have already briefly discussed the geographic and climatic conditions of the Proplateau region, so there remains to be considered onl}' the environmental conditions in the Texas portion of the range of this form. This region may for convenience be divided into two physiographic regions; the prairie-plains region, situated roughly to the east of the Pecos River, north of the thirtieth parallel and west of the ninety-eighth meridian, and the Rio Grande plain, which occupies the triangular area between the prairie-plains, Rio Grande River, and ninet3'-eighth. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States National Museum; Smithso
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