1886.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 409 



A NE"W STUDY OF THE GENUS DIPODOMYS. 

 Br FREDERICK W. TRUE. 



(Read before the Biological Society of Washington, November 28, 1885.) 



The genus Dipodomys was iutroducecl into the literature by Dr. J. E. 

 Gray in 1841. He described the typical species under the name of 

 D. phillipii (afterward changed to D. pMllipsii) from Mexican speci- 

 mens (Ann. & Mag. N. H., vii, 1841, p. 521). 



In 1846 Wagner described the same genus under the name of Macro- 

 colus halticus, and gave an account of the skeleton. His specimens were 

 also from Mexico (Arch, fiir Naturgesch., 1846, i, 176). 



In 1848 Dr. William Gambel described a new species, under the name 

 of I), agilis, from specimens from the Pueblo de los Angeles, California. 

 (Proc. Acad. Nat. Sci. Phila., 1848, p. 77). 



In 1853 another species, called D. Ordii, was added to the list by Dr. 

 S. W. Woodhouse, who discovered it at El Paso, on the Eio Grande. 

 (Sitgreave's Exped. to the Zuni and Colorado Eivers, 1853, p. 50, pi. 4.) 



In the same year Dr. Le Conte revised the genus and added two 

 species, viz, D. Heermanni and D. Wagneri (Proc. Acad. Nat. Sci. Phila., 

 1853, p. 224). 



In 1855 Professor Baird made known a sixth species, D. montanus 

 from Fort Massachusetts. 



Two years later the genus was revised a second time by Professor 

 Baird, who placed the M. halticus of Wagner, with a mark of interro- 

 gation, under the D. pMllipsii of Gray, regarded his own D. montanus as 

 questionably synonymous with the D. Ordii of Woodhouse, recognized 



D. agilis as a distinct species, and dismissed D. Eeermani and D. Wag- 

 neri with the remark that he knew nothing of them. (Rept. U. S. Pacific 



E. E. Survey, 1857, 406 et seq.) 



In 1875 the genus was again reviewed bj^ Dr. Coues, who united all 

 the species under the D. philUpsi of Gray, but recognized a variety of 

 the same, which he styled D. phillipsi ordi (Proc. Acad. Nat. Sci. Phila., 

 1875, p. 305 et seq.). 



After so much elaboration, it would seem as if the subject of the 

 taxonomy of this genus must be exhausted, and I should owe an apology 

 for again calling attention to it were it not that I have discovered, upon 

 examination of the series of specimens in the National Museum, a char- 

 acter, which appears to have been hitherto overlooked, and by which it 

 becomes possible to divide the genus into two very distinct sections. 



This character relates to the number of hind toes. In one series of 

 specimens the hallux, though reduced in size, is perfectly formed and 

 bears a rounded claw. In the other series the hallux, including the 

 metatarsal, is entirely absent, and the hind foot has, therefore, but four 

 toes. 



