SACCOMYIDJS— DirODOMYIN^E— DIPODOMYS. 539 



This second table, as far as it goes, leads to some tangible and practical 

 results. More specimens would undoubtedly modify the exact figures, but 

 would, I think, only confirm the general statement, that there is a decided 

 difference in relative length of head and body and of tail between specimens 

 from the interior and those from the coast region— just as there is in the 

 genus Ciketodipus. This substantiates, in effect, the broad distinction estab- 

 lished by Baird in 1857, though the details given by that author require 

 qualification.* 



In the animals from the interior, with an average length of nearly 4.50 

 inches, the tail is scarcely or not an inch longer than the body; that is to say, 

 it is about one-fourth as long again as the head and body. 



In the coast region specimens, with an average length of less than 4 

 inches, the tail is about 2 inches longer than the head and body; that is to 

 sa} r , it is, if anything, more than half as long again as the body. 



The feet do not present any very tangible characters. We find them of 

 all sizes, coupled with different extremes of tail length. Nevertheless, it will 

 be observed that the Cape St. Lucas specimens alone of the coast series pre- 

 sent small feet, under 1.50; and that, without these, the coast series would 

 show a length of foot of 1.G0-1.70, thus correlated with the greater length 

 of tail. 



To these data may be added some others, tending to substantiate a dif- 

 ference between the two forms of the genus. The western animal averages 

 smaller and of more slender build, with larger ears and longer limbs, and 

 especially longer tail. It is darker in color, the prevailing tone being a mouse- 

 brown, overcast with tawny or fulvous. The animal from the interior is larger, 

 and noticeably more stoutly built, with smaller ears and shorter limbs, and 

 particularly shorter tail. It is lighter in color, the prevailing tone being the 



* Mamm. N. Am. 1857, p. 409.—" Whatever the number of species, all hitherto detected in North 

 America belong to the two following sections : — 



" Section I. Hind foot not exceeding 1.50 inches, usually appreciably less ; about one-third tho 

 length of head and body. Tail vertebrae about 1J times the length of head and body in nature ; rarely 

 exceeding 5 inches, never 5£. D. ordii. 



" Section II. Hind foot, 1.60 iuches, sometimes more ; always considerably exceeding 1.50 ; almost half 

 as long as head and body iu the first specimens. Tail vertebras If times the length of head and body, 

 always exceeding 5J inches ; usually from 6 to 7 iuches. D. phillippi, D. agilis." 



The proportions of body and tail here laid down I verify exactly, though the limits of extremes 

 given require to be enlarged. On the contrary, the statements made respecting the feet do not hold, 

 upon examination of more material. In fact, the Cape St. Lucas are the shortest-footed animals of tho 

 whole seriee ; and in one very largo Texas specimen (dry), not giveu iu tho table, the foot is almost 2 

 inches long. 



