VARIATIONS OF GARTER-SNAKES. 61 



tion, except on the higher suinmits. The flora of the phiins and the 

 slopes below tlie timber zones consists of such forms as the sotol, 

 ocotillo, creosote-bush, mesquite, and a host of cactuses. 



To the east of the East Front Ranges the climate becomes pro- 

 gressively more moist than that of the Proplateau region, although the 

 rainfall continues l)elow 30 inches to the ninety-eighth meridian. On 

 the sandy ])lains of the lower Rio Grande, with its dense growths of 

 chaparral and intervening prairies, the conditions are still very arid, 

 owing to the low humidity and small rainfall, but to the eastward 

 the grasses become more meso])hytic and grade into the eastern for- 

 ests near the 98th meridian. To the northward the forest margin is 

 bordered on the west by the mesophytic grass associations of the 

 prairies that rise to the westward to the solid buffalo grass forma- 

 tion of the high plains. 



The ninety-eighth meridian, as has been pointed out l)y Hill (1900) 

 and in more detail by Bray (1901 and 1904), and Bailey (1905), marks 

 in a general way the boundary between the mesophytic forest of 

 southeastern United States and the great grass country of Texas. 

 This doubtless marks equally well the dividing line between the 

 fauna of these two areas. As Bailey has shown, it marks the eastern 

 limit of the mesquite, Texan woodpecker, and Texas rattlesnake. 



Owing to the extreme paucity of records, it is impossible to draw 

 the geographic boundaries of marcianus, except in a ver}^ general 

 way. The range has been defined by Cope (1892, 656) as ''restricted 

 to the valley of the Rio Grande from Colorado to its mouth, extend- 

 ing eastward into Texas as far as the Concho and Nueces rivers," 

 but as specimens have been taken in Arizona, the range as given by 

 Brown (1901, 24), ''Central Texas to western Arizona" is more 

 nearly correct. But little importance can be placed in l(K'ality 

 records for this form until the specimens have been examined. In 

 1875, Yarrow (1875, 573), in writing of this form, remarked that the 

 last specimens of vagrans (elegans) seen were at Taos, New Mexico, 

 on the north side of the Picoris Mountains, while on the south side of 

 these mountains marcianus was said to occur for the first time, and 

 specimens were listed from "San Ildefonso, New Mexico," "Abiquiu, 

 New Mexico" (3), "Taos, New Mexico," and "Pueblo, Colorado" (2). 

 Unfortunate!}" "rily field numbers are given for these specimens, 

 so that they cannot be located with certainty, but the only speci- 

 mens in the U. S. National Museum from these localities bearing the 

 date and collectors recorded by Yarrow are three specimens of ele- 

 gans from Abiquiu (No. 8728), one specimen of elegans labeled "New 

 Mexico" (No. 8421), and two specimens of radix from Pueblo (No. 

 8581). The particular specimens from San Ildefonso listed by Yar- 

 row as marcianus cannot be determined with certainty, as there are a 

 number of specimens in the U. S. National Museum bearing the same 



