SACCOMYID^E— CHARACTERS OF TIIF FAMILY. 41)1 



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. Cricetodipus, 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. 



Family SACCOMYIDA. 



< Saccomyina, Waterhoi'SE, Nat. Hist. Mamm. ii, 1848, 8. (As a group of Muridcc. Included the Geomyida; 



now made a separate family ; equivalent to the " superfamily " Saccomyoidea of Gill, 1872.) 



< Pseudosiomidcc, Gervais, " Diet. Univ. d'Hist. Nat. xi, 1848." (Family. Equivalent to the Saccomyina 



of Waterhouse.) 



< Saccomyida; Lilljeborg, Syst. OEfv. Gnag. Daggdj. 1866. (Family. Equivalent to Saccomyina of 



Waterhouse.) 

 = Saccomyina;, Baird, Mamm. N. Am. 1857, 404. (Suhfamily of Saccomyida; which, with this author, 



included Geomyida; Baud's family Saccomyida; being equivalent to Saccomyina, Waterh.) 

 = Saccomyina; Gray, Proc. Zool. Soc. 1868, 199. (Spoken of as a " family ", though terminology indicates 



subfami.ly.) 

 = Saccomyida; Gill, Arraug. Fam. Mamm. 1872, 21. (Family.) 

 — Saccomyida; Coues, Proc. Phila. Acad. 187. r i,274. (Family.) 

 = Hctcromyina; Alston, Proc. Zool. Soc. Lond. 1876, 88. (Subfamily. Equivalent to Saccomyina; of 



Baird and Saccomyida of Gill and Coues.) 



Chars.*— 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 uo 

 material modification of the phrase is requited to embrace Heloromys — excepting probably some of the 

 cranial features, especially those of the temporal region. Special reference is had to antithesis with 

 Geomyidce. 



