324 PROCEEDINGS OF THE ACADEMY OF 



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. This substantiates, in effect, the 

 broad distinction established by Baird in 1857, though the details 

 given by that author require qualification. 1 



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 bodj^. 



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

 than 4 inches, the tail is about two inches longer than the head 

 and body ; that is to say, 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 present small feet, under 1.50 ; and that 

 without these, the coast series would show a length of foot of 1.60- 

 1.70, thus correlated with the greater length of tail. 



To these data mciy be added some others, tending to substan- 

 tiate the differentiation of the forms of the genus. The western 

 animal averages smaller, and of more slender build, with larger 



1 M. N. A. 1858, p. 409. "AVhatever 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 the length of head and body. Tail vertebrae about 1 times 

 the length of head and body in nature ; rarely exceeding 5 inches, never 5. 

 D. ordii. 



"Section II. Hind foot, 1.60 inches, sometimes more ; always considerably 

 exceeding 1.50 ; almost half as long as head and body in the first specimens. 

 Tail vertebras If times the length of head and body, always exceeding 5| 

 inches; usually from 6 to 7 inches. D. phillipjn, 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 the 

 whole series : and in one very large Texas specimen (dry), not given in the 

 table, the foot is almost 2 inches long. 



