SACCOMYID—PRELIMINARY CONSIDERATIONS. 489 
each should rank as a family; for, as I have already attempted to show, * 
the great difference im configuration between the Geomyid@e and Saccomyide, 
though only a matter of secondary consequence, is codrdinated with struc- 
tural characters important enough to warrant the erection of the subfamily 
Sacconyine into a family Saccomyide, distinct from, though unquestionably 
standing next to, the family Geomyrde. 
It may be conceded that this valuation was virtually, if only incidentally, 
set forth in 1868 by Dr. J. KE. Gray,t who, though using a terminology (“ Sac- 
comyine”) indicative of a subfamily, nevertheless speaks of “the family” of 
Pouched Mice, from which Geomys and Thomomys are excluded. 
Tu 1872, Dr. T. Gillf first formally recorded a family Saccomyide as 
equivalent to the subfamily Saccomyine of Baird, 1857, and of Gray, 1868, and 
to the subsequent Heteromyine of Alston, 1876. The group thus accorded 
full family rank was placed next to the family Geomyide, 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 Saccomyide as 
endorsed by Baird. Such term, Saccomyoidea, may be aecepted as an expres- 
sion of the unquestionable fact that the Saccomyide and the Geomyide 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 Saccomyide so 
drawn as to exclude Geomyide, | 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 treited 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, 
Perognathus 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. Sury. Terr. 2d ser. No. 2, 1875, pp. 83 seq. ; and Proc. Acad. Phila. 
1875, pp. 272 seq. 
t Synopsis of the Species of Saccomyinz, or Pouched Mice, in the Collection of the British Museum. 
< Proc. Zod). Soc. Lond. 1868, pp. 199-206. 
{ Arrangement of the Families of Mammals. With Analytical Tables. Prepared for the Smithsonian 
Institution. < Smiths. Mise. Coll. No. 230. (8vo, Washington, 1872. 
§ Remarks on the Genus Dipodomys and Perognathus. < Proc. Phila. Acad. vi, 1853, pp. 224, 225 
|| Mammals of North America, pp. 405-426. 1857. 
** Monatsh. kGuigl. preuss. Akad. Wissensch, Berlin, Mai 1874, p. 355. 
