Geomys fontanelus Sherman, 1940. Jour. Mamm., 21:341, August 13. Type from 7 mi. NW Savannah, Chatham County, Georgia.
1895. Orthogeomys Merriam, N. Amer. Fauna 8:172, January 31.
1895. Heterogeomys Merriam, N. Amer. Fauna 8:179, January 31 (type, Geomys hispidus Le Conte, 1862).
1895. Macrogeomys Merriam, N. Amer. Fauna 8:185, January 31 (type, Geomys heterodus Peters, 1865).
Type.—Geomys scalops Thomas, 1894, from Tehuantepec, Oaxaca, México.
Chronologic range.—Late Pleistocene Wisconsin deposits (San Josecito Cave local fauna, Nuevo León, México) to Recent.
Description and discussion.—Species of this genus are of medium to large size. The skull is strongly dolichocephalic in most species; the posterior part of the skull is especially narrow. The angular processes are remarkably short, especially in relation to the length of the mandible. The nasals and rostrum are relatively broad and heavy. The pelage is coarse, and often hispid. In some species the hairs are so sparsely distributed that the body appears almost naked, and none has so dense a covering of hair as do other genera. The genus occurs entirely within the tropical life-zones, and most of the external features seem to be associated with adaptation to tropical conditions.
The upper incisor is unisulcate; the sulcus is usually near the inner border of the tooth, but in some species (subgenus Orthogeomys) it is more medial, and in a few individuals with an extremely wide groove the outer lip of the sulcus may actually reach the middle of the tooth. The groove is compressed or open. The premolar is a double column united at the mid-point. The two prisms are of approximately equal size, and the lateral re-entrant folds are so compressed that their sides are parallel. Enamel plates cover the anterior surface and border the re-entrant angles in both upper and lower premolars. As in other members of the tribe, the lower premolar has a fourth enamel plate on the posterior surface of the posterior lophid. In the upper premolar, the enamel plate is reduced to a narrow blade on the lingual side of the loph as in the living species of the genus Zygogeomys. In the subgenus Orthogeomys the posterior plate is usually absent, and otherwise is narrow and near the lingual border of the tooth.
Each lower molar, in the final stage of wear, consists of a single elliptical column having an enamel plate only on the posterior surface. The first and second upper molars are single elliptical columns having one enamel plate on the anterior surface and another on the posterior surface. The plates are separated by a tract of dentine on each side of the tooth. The third upper molar is partly bilophodont, and the two lophs are separated by a deep outer re-entrant fold. In many of the species an inner re-entrant fold also is retained, but in the adult tooth it is less distinct than the outer. In all of the species the posterior loph is long and forms a conspicuous heel; consequently the crown is significantly longer then wide. Moreover, the posterior loph has an enamel plate on each side. The labial plate always borders the outer re-entrant fold, and in the subgenus Orthogeomys is infrequently separated into two small plates.