Dentition.—The incisors are narrow and compressed as in the genus Mus, but they are less deep from front to back; those of the upper jaw (Plate 33. fig 2. b.) have each a distinct longitudinal groove, which is situated nearer to the outer than to the inner edge of the tooth. Close to the inner edge of each of these teeth an indistinct second longitudinal groove may be seen by means of a lens. The lower incisors are nearly equal in width to the upper.
The crowns of the molar teeth in the young Reithrodon are higher than in Mus, and they are rootless; in the adult animal, however, they possess distinct roots. The folds of enamel form sigmoid flexures, are closely approximated to each other, and those of the opposite sides of the tooth meet.
1. Reithrodon cuniculoïdes.
Plate XXVI.
Reithrodon cuniculoïdes, Waterh., Proceedings of the Zoological Society of London for February 1837, p. 30.
R. suprà griseus, flavo-lavatus, pilis nigris intermixtis; abdomine guláque pallidè flavis; natibus albis; pedibus albis; auribus mediocribus, intùs pilis flavis, extùs pilis pallidè flavis, obsitis; pone aures, notâ magnâ albescenti-flavâ; caudâ corpore breviore, suprà pallidè fuscâ, subtùs albâ.
Description.—Head rather large and arched; ears moderate; tail nearly as long as the body; tarsi rather long; fur long and very soft. General tint of the upper parts of the body grayish brown, with a considerable admixture of yellow; of the sides of the body grayish tinted with yellow; the lower portion of the cheeks, and the lower half of the sides of the body are of a delicate yellow colour; the under parts of the head and body are yellowish white; the fore part of the thighs is whitish; the rump, feet, and tail are white, excepting the upper surface of the latter, which is brown; behind each ear there is a patch of yellowish white hairs. The ears are tolerably well clothed with hairs; those on the inner side are for the most part of a yellow colour, but towards the posterior margin they are brown; externally, the hairs are also yellow, excepting on the fore part, where they are dusky brown. The hairs of the moustaches are very long and numerous; black at the base, and grayish at the apex. The feet are well clothed with hairs which cover and nearly hide the claws; the under side of the tarsus is clothed with grayish brown hairs. The tail is well clothed with tolerably long hairs which completely hide the scales. The hairs on the back are of a deep gray colour at the base, broadly annulated with yellow near the apex, and dusky at the apex: the longer hairs are black: on the throat and belly the hairs are deep gray at the base, and broadly tipped with pale yellow—towards the cheeks and sides of the body with a deeper yellow. The incisors are yellow.
| In. | Lines. | ||
|---|---|---|---|
| Length | from nose to root of tail | 6 | 5 |
| of tail | 3 | 3½ | |
| from nose to ear | 1 | 4 | |
| of tarsus (claws included) | 1 | 4¼ | |
| of ear | 0 | 7 |
Habitat, Patagonia, (April and January).
In the arched form of the head this little animal bears considerable resemblance to a young rabbit, a resemblance which has struck almost all who have seen it, I have therefore applied to it the specific name Cuniculoïdes. The skull is figured in Plate 33, fig. 2. a., its dimensions are as follows:—
| In. | Lines. | ||
|---|---|---|---|
| Total | length | 1 | 4 |
| Width | 0 | 10 | |
| Length | of nasal bones | 0 | 7 |
| of incisive foramina | 0 | 4¾ | |
| Distance between the outer surface of the incisors and the front molar upper jaw | 0 | 5 | |
| Longitudinal extent of the three molars of the upper jaw | 0 | 3¾ | |
| Length | of a ramus of the lower jaw, without the incisor | 0 | 9¾ |