SACCOMYIDAi—CHARACTERS OF THE FAMILY. 49] 
a subgenus of Perognathus, upon certain obvious and eligible external char- 
acters alone. But examination of the skull, which, it seems, that author did 
not make, has satisfied me that the cranial peculiarities are fully up to a cur- 
rent generic mark. C7icetodipus, in fact, makes a decided step away from 
Perognathus in the direction of Dipodomys, though still falling far short of 
the exaggerated peculiarities of the latter. 
j) e / 
Famity SACCOMYIDAL. 
< Saccomyina, WATERHOUSE, Nat. Hist. Mamm. ii, 1848,8. (Asa group of Mwridaw. Included the Geomyida, 
now made a separate family; equivalent to the ‘superfamily ” Saccomyoidea of Gill, 1872.) 
< Pseudostomide, GERVAIS, “ Dict. Univ. d’Hist. Nat. xi, 1848.” (Family. Equivalent to the Saccomyina 
of Waterhouse.) 
< Saccomyide, LittsEBoRG, Syst. Gify. Gnag. Diiggdj. 1866. (Family. Equivalent to Saccomyina of 
Waterhouse.) 
= Saccomyine, BarrD, Mamm. N. Am. 1857, 404. (Subfamily of Saccomyidew, which, with this author, 
included Geomyida@, Baird’s family Saccomyide being equivalent to Saccomyina, Waterh.) 
= Saccomyinw, GRAY, Proc. Zodl. Soc. 1868, 199. (Spoken of asa “ family ”, though terminology indicates 
subfamily.) : 
= Saccomyida, GILL, Arrang. Pam. Mamm. 1872,21. (Family.) 
= Saccomyide, Cours, Proc. Phila, Acad, 1875, 274. (amily.) 
= Heteromyine, ALSTON, Proc. Zod). Soc. Lond. 1876, 88. (Subfamily. Equivalent to Saccomyine of 
Baird and Saccomyide of Gill and Coues.) 
Cuars.*—Skull light, thin, and papery, with few, if any, decided angles 
or ridges; rostrum elongate, attenuate, and tapering; nasals projected beyond 
incisors. Intermastoid width not less than the interzygomatic, sometimes 
much greater. Interorbital space much wider than the rostrum. Occipital 
region formed largely or mostly of the mastoids. Palatal surface nearly flat 
and horizontal. No anteorbital foramen in a usual site, but a large, rounded 
perforation of the side of the maxillary instead. Zygomata slender, depressed 
in position, almost or quite abutting behind against the tympanic; malar 
thread-like. A delicate scroll-like lachrymal, easily detached. Frontal broadly 
trapezoidal. Parietal broad, triangular or pentagonal. A large interparietal, 
embraced betwixt forks of the occipital. Squamosal almost entirely restricted 
to the orbit. Tympanic more or less inflated. Mastoid enormously enlarged 
and bullous, mounting to the top of the skull, and also forming much or most 
of the occipital surface, the occipital bone itself being correspondingly 
reduced, and scarcely forming part of the general occipital surface. Petrosals 
moderately inflated, their apices closely approximated or even in mutual con- 
tact. Coronoid process of mandible slender, sloping, prickle-like, scarcely 
*Drawn from Perognathus, Cricetodipus, and Dipodomys ; but there is reason to believe that no 
material modification of the phrase is required to embrace Heleromys—excepting probably some of the 
cranial features, especially those of the temporal region, Special reference is had to antithesis with 
Geomyida, 
