1874.] 279 [Allen. 



decreases in intensity, Nebraska specimens being much paler than 

 those taken on the same parallel near the Mississippi River. Speci- 

 mens from the Indian Territory are also very much paler than those 

 from St. Louis, as are Texas ones than those from Louisiana. Even 

 between specimens from the prairies of northwestern Louisiana and 

 others from the lowlands of the same State, near the Mississippi 

 Eiver, the difference in color is very strikingly marked. 



The variation in color occurring in representatives of the same 

 species at localities differing in longitude, is well shown in quite a 

 number of groups. But few specific forms, however, have a suffi- 

 ciently wide range to illustrate the variations that obtain along a given 

 parallel throughout the whole breadth of the continent, the Sciuras 

 hudsonius group being the only instance among the squirrels. Oth- 

 ers, however, show the transition that obtains in passing from the 

 moist, fertile prairies of the Mississippi Valley to the dry plains, or 

 from the deserts and mountainous districts of the interior to the moist 

 region bordering the Pacific Coast north of the parallel of 40°. 

 Spermopliilus tridecem-lineatus furnishes a good illustration of the dif- 

 ferences in color that occur between representatives of the same spe- 

 cies living on the moist, fertile prairies and those inhabiting the dry, 

 barren plains, those from Illinois, Wisconsin, Minnesota and Iowa 

 being much darker than those from Western Nebraska, Western 

 Kansas and Colorado. P^ven specimens from Eastern Kansas are 

 much darker than those from the middle and western portions of the 

 same State. In this species the color is varied, in passing from the 

 prairies to the plains, not only by the lighter shade of the dark 

 ground color, but by the considerably greater breadth of the light 

 spots and stripes in the specimens from the plains. The Spermoplii- 

 lus grammurus group (composed of the S. grammurus, S. Beecheyi, S. 

 Douglassi, etc., of authors) illustrates not only a similar variation in 

 intensity of color between the inhabitants of dry and moist regions, 

 but also a somewhat changed style of coloration. Beginning with the 

 nearly uniformly gray or grizzled type of Texas and Southeastern 

 New Mexico, we pass to the more rufous or reddish phase of the cen- 

 tral portions of the Rocky Mountains (in Colorado), which also has an 

 increased amount of hoariness on the sides of the neck and shoulders, 

 to the form west of the Sierra Nevada Mountains, typically represent, 

 ing the Spermopliilus Beecheyi, in which the hoariness forms broad 

 lateral bands separated by a narrow brown medial stripe. This 

 form in Northern California passes into the so-called Spermopliilus 



