158 GLIRES. 
Hab. Mexico, Jalapa (de Oca, U.S. Nat. Mus.?), Tuxpango (Sumichrast, ib.?). 
This very dark and glossy-furred Vole was first described by Dr. Coues as a variety of 
the last species!; but he subsequently convinced himself that it was quite distinct ?. 
Reluctance to injure the type specimens unfortunately prevented his describing the 
skull and teeth; and further observation is consequently required before its relation- 
ship with A. pinetorum is set at rest. 
Fam. IV. GEOMYIDA. 
1. GEOMYS. 
Geomys, Rafinesque, Am. Month. Mag. ii. p. 45 (1817, fide Baird, Mamm. N. Am. p. 368). 
Diplostoma, Rafinesque, loc. cit. 
Saccophorus, Kuhl, Beitr. Zool. &c. p. 65 (1820). 
Pseudostoma, Say, Long’s Exped. i. p. 406 (1823). 
Ascomys, Lichtenstein, Abh. Ak. Berl. 1822-23, p. 20 (1825). 
The family Geomyide is distinguished, among other characters, by the possession of 
cheek-pouches which open externally on the sides of the face, and are not connected with 
the mouth—a structure which is not found in any other known Mammal. In geogra- 
phical distribution it is principally Nearctic; but all the five genera are represented in 
our subregion. The group presents two very distinct types, which have been sometimes 
regarded as deserving of full family rank; but in spite of the arguments of Dr. Coues in 
favour of that course*, I still hold to the view that they may best be treated as sub- 
families under the names Geomyine and Heteromyinef. 
Of these the first contains thickset fossorial animals with short limbs and tails, rudi- 
mentary ear-conchs, and massive skulls, in which the mastoids do not appear on the top - 
of the cranium, and the zygomatic arches are stout and divergent. They fall naturally . 
into two genera :—Geomys, with deeply channelled incisors, and very large fore feet and 
claws; and Thomomys, in which the incisors are either plain or only slightly grooved 
near the margin, the fore feet moderately developed, and ‘the skull less massive. 
* See his observations, Proc. Ac. Philad. 1875, pp. 130-138, 272-327 ; Powell’s Exploration of the Colo- 
rado River, pp. 217-285; and Mon. N.-Am. Rodent. pp. 487-542, 607-629; which contain very detailed 
descriptions of the anatomy and characters of the known genera and species. 
+ Cf. P.Z.8. 1876, p. 69. With regard to the name of the latter subfamily it may be observed that 
Dr. Coues appears to think it unnecessary to change Saccomyine, Baird, into Heteromyine, Alston. Dr. Coues 
himself confesses that there is “no doubt” that Saccomys is only a synonym of Heteromys; and it appears to 
me that the laws of nomenclature and of convenience both require that the latter name should be used in com- 
posing the title of any superior group. | 
