410 



THE GENUS DIPODOMYS. 



In the original descriptions of the various species the references to 

 this character are as follows : 



Species. 



Locality. 



D. phillipgii Gray 



M. halticus Wagner 



2). agilig Ganibi'l 



D. Ordii Wooilhouse 



2). nierma%in Le Coute 



jD. Waijiicri Le Conte 



2). montanus Baird 



Mexico. 



Do. 

 Calil'oinia. 

 Rio Grande. 

 Sieira Nevada. 



Fort Massachuae.tts. 



■ In the figure. 



t Not mentioned. 



The only remark regarding the toes in Gray's original diagnosis of 

 the genus is as follows: "Toes, 5-4." 



Wagner, on the other hand, enters more into detail. Speaking of the 

 hind teethe says : " DieDaumeuzehe fehlt zugleich mit ihrem Mittelfuss- 

 knochen; jede der 4 anderu Zehen hat ihre gewohnlichen Phalangen."* 



Again, on comparing his new genus with Dipns, Scirtetes, and Jaculus, 

 he writes: " Von diesen alien unterscheidet ihn schon dieBeschaffenheit 

 seines Gebisses; von letzterem liberdies der Um stand, dass die Hinter- 

 fiisse nur 4 zehig und der Schwanz dichter behaart ist."t Finally among 

 his generic characters is the following: " Pedes posteriores 4 dactyli."J 



Gambel, in his description of D. agilis, dismisses the character with a 

 single phrase, as follows : " Both hind and fore feet with four toes and 

 the rudiment of a fifth." § 



Of the monographers of North American mammals who have written 

 since 1848, Audubon & Bachman (who had access to and figured Gray's 

 type) give the genus four hind toes, while Professor Baird and Dr. Coues 

 give it five hind toes. The discrepancy seems not to have been hither- 

 to detected. 



It will be conceded, I believe, that the presence or absence of the 

 hallux is a character of more importance than those relating to the 

 proportions of the feet and tail and the variation of color. || If it be 

 accorded specific rank, the two species resulting from the division of 

 the genus must, I am persuaded, stand in the nomenclature hereafter 

 under the names of JJ. phiUipsii Gray, and Z>. agilis Gambel, the former, 

 with four hind toes, being the type of the genus; and the latter, the first 

 of the subsequently described species in which the possession of five 

 hind toes is distinctly recognized. 



* Wiegman's Archiv, 1846, i, p. 175. 



tL. c. 



tOp. cit., p. 27(i. 



§ Proc. Acad. Nat. Sci., 1848, p. 78. 



II The absence of the thumb has, indeed, been employed as a negative character of 

 generic value, but Dr. Dobson has recently pointed out the inadvisability of such a 

 course. 



