SACCOMYIDCE— PRELIMINARY CONSIDERATIONS. 489 



each should rank as a family; for, as I have already attempted to show,* 

 the great difference in configuration between the Geomyidce and Saccomyidce, 

 though only a matter of secondary consequence, is coordinated with struc- 

 tural characters important enough to warrant the erection of the subfamily 

 Sacconiyince into a family Saccomyidce, distinct from, though unquestionably 

 standing next to, the family Geomyidce. 



It may be conceded that this valuation was virtually, if only incidentally, 

 srt forth in 1868 by Dr. J. E. Gray.f who, though using a terminology (" Sac- 

 comyina} v ) indicative of a subfamily, nevertheless speaks of "the family" of 

 Pouched Mice, from which Geomys and Thomomys are excluded. 



In 1872, Dr. T. Gill J first formally recorded a family Saccomyidce as 

 equivalent to the subfamily Saccomyina of Baird, 1857, and of Gray, 1868, and 

 to the subsequent Heteromyince of Alston, 1876. The group thus accorded 

 full family rank was placed next to the family Geomyidce, the two together 

 constituting one of the author's numerous taxonomic refinements, a "super- 

 family" (or series) Saccomyoidea, which was hence exactly equivalent to the 

 group Saccomyina as founded by Waterhouse and the family Saccomyidce as 

 endorsed by Baird. Such term, Saccomyoidea, may be accepted as an expres- 

 sion of the unquestionable fact that the Saccomyidce and the Geomyidce are 

 more intimately related to each other than they are to any other family of the 

 Rodents. 



Thus following Professor Gill in determining a family Saccomyidce so 

 drawn as to exclude Geomyidce, I wish, before giving my characterization of 

 the group, to note what disposition has been made of its component genera 

 by several authors. Dr. LeConte, in 1853, § and Professor Baird, in 1857, || 

 both tre tted only of North American forms, recognizing but, two genera, 

 Dipodomys and Perognathus (+subg. Cricetodipus). Dr. Gill made no sub- 

 division of the family. Mr. Alston recognized three genera, — Dipodomys, 

 Perognallius and Heteromys. Dr. Gray, and, following him, Hr. Peters,** 

 divided the Pocket Mice into two groups of no assigned value, namely, 



" Bulletin U. S. Geol. and Geogr. Surv. Terr. 2d ser. No. 2, 1875, pp. 83 seq. ; and Proc. Acad. Phila. 

 1875, pp. 272 seq. 



t Synopsis of the Species of Saccomyina), or Pouched Mice, in the Collection of the British Museum. 

 .<Proc. Zool. Soc. Loud. 1888, pp. 199-206. 



t Arrangement of the Families of Mammals. With Analytical Tables. Prepared for the Smithsonian 

 Institution. < Smiths. Misc. Coll. No. 230. (8vo, Washington, 1872.) 



§ Kemaiks on I lie Genus Dipodomys and Perognathus. < Proo. Phila. Acad, vi, 1853, pp. 221, 225 



|| Mammals of North America, pp. 405-426. 1857. 

 ** Mouatsh. kiiuigl. prouss. Akad. Wisseusch. Berliu, Mai 1871, p. 355. 



