SIZE.—About 2¾ inches; tail, about 2 inches.—'Mammifères,' p. 291.
| Dentition of Arvicola. |
In this sub-family the molars are generally semi-rooted or rootless. The Arvicolinæ or Voles consist of the American Musquash (Fiber zibethicus), a very beaver-like water rat of large size; the Lemmings (Myodes), of which there are several species which are celebrated for their vast migrations; and the true Vole (Arvicola), which is the only genus found in India, and then only in the colder climate of the Himalayas. There are several species in Europe, of which three are found in England. According to Professor Dallas, the true Voles number about fifty species, arranged by various writers under a considerable number of sub-genera. In India we have only eight known species, and two more from the adjacent country of Thibet.
The European forms of Arvicolæ have been divided by Blasius into four sub-genera of two divisions—the first division having rooted molars in the adult animal—containing one sub-genus only, Hypudæus of Illiger; the second division consists of three sub-genera with rootless molars, viz. Paludicola, Agricola, and Arvicola, which last has again been subdivided into long-eared and short-eared Voles—Arvicola and Microtus—distinguished by the former having eight and the latter four mammæ, and respectively six and four tubercles on the plantæ, the ears of the latter being almost hidden by the fur.
None of the forms with which we have now to deal belong to the first division, for, as far as the matter has been investigated, the Indian Voles have rootless molars, but the character of the teeth in some differs from the European forms, and therefore Mr. Blanford has proposed a new section, Alticola, for their reception. I have not space here, nor would it accord with the popular character of this work, to go minutely into all the variation of dentition which distinguish the different species. To those who wish to continue to the minutest details the study of the Indian Voles, I recommend a most careful and elaborate paper on them by Mr. W. T. Blanford, F.R.S., in the Journal of the Asiatic Society of Bengal, vol. L., pt. ii.; but without entering into the microscopic particulars of each species, I may here give a general idea of the formation of the teeth of the Arvicolæ differing as it does so much from others of the myomorphic or mouse-like group of rodents. In these the general contour of the molar teeth is roundish oblong, the margins being wavy or indented, according to the convolutions of the enamel, but in the Voles there is a sharp angularity about these indentations; the marginal lines, instead of being in well-rounded curves, are sharply zigzag, forming acute angles. If you were to draw two close parallel zigzag lines it would give you some idea of the contour of these teeth. The molars are in fact composed of alternating triangular prisms, with the outer folds of enamel forming deep and acute angles. The other characteristics of this family are: skull, with brain case rhomboidal, frontals much contracted; infra-orbital opening typical; limbs moderate; tail moderate, or short and hairy.
Muzzle blunt; fore-feet small, with short claws; soles naked; tail longer than the hind-foot, clad with short hairs; incisors plain, smooth in front. The fore-feet in some species have but a small wart in place of a thumb; in others there is a small thumb with a minute claw. The hind-feet have five toes.
[NO. 387. ARVICOLA STOLICZKANUS.]
The Yarkand Vole.