3. Reithrodon chinchilloides.
Plate XXVII.
R. vellere longissimo et mollissimo; corpore suprà et ad latera cinereo, flavescenti-fusco lavato, subtùs flavescenti-albo; caudâ corpore breviore, suprà fuscâ, subtùs albâ: auribus parvulis: tarsis mediocribus.
Description.—Ears small; tail shorter than the body; tarsus moderate; fur long and extremely soft. General hue of the upper parts of the head and body ashy-brown; the lower part of the cheeks and sides of the body are of a delicate yellow colour; the under parts of the head and body and the rump are cream colour. The ears are blackish;[[27]] the tail is tolerably well clothed with longish hairs, which are, however, not so thickly set as to hide the scales—on the upper side they are blackish brown; on the sides and beneath they are white. The feet are white. All the fur is of a deep gray colour at the base; the hairs of the back are of a very pale yellow colour (almost white) near the tip, and brown at the tip; the longer hairs are black at the apex. The incisors are yellow; the hairs of the moustaches are numerous and very long—some of them are whitish, and others are black at the root, and gray at the apex.
| In. | Lines. | ||
|---|---|---|---|
| Length | from nose to root of tail | 5 | 0 |
| of tail | 2 | 4 | |
| from nose to ear | 1 | 2 | |
| of tarsus (claws included) | 1 | 0 | |
| of ear | 0 | 5½ |
Habitat, South shore of the Strait of Magellan, near the Eastern entrance.
This little animal was preserved in spirit, and has since been mounted, it is probable, therefore, that the colours have been slightly changed. It is of a smaller size than either of the preceding species. Its fur is long, extremely soft, and somewhat resembles that of the Chinchilla. The ears are smaller, and the tail is shorter, and less densely clothed with hairs than in Reithrodon cuniculoides. The skull (see Plate 43, fig. 20, a, 20, b, and 20, c,) differs in many respects from that of the species last mentioned. It is of a smaller size, the nasal portion is proportionately shorter and narrower, the incisive foramina are shorter; the pterygoid processes do not approximate so nearly at their base, and the pterygoid fossæ are very shallow, whereas in R. cuniculoides they are deep. In the skull of the animal just mentioned there are two distinct longitudinal grooves on the palate, which extend backwards from the incisive foramina, and terminate in two rather large and deep excavations: these excavations are in the palatine bone, and situated between the last molar teeth; they are separated from each other by a narrow, longitudinal, elevated ridge; a narrow ridge also separates them from the pterygoid fossæ. At the bottom of each of these hollows are several minute foramina, and in front of them there are two larger longitudinal foramina. In R. chinchilloides, the longitudinal grooves on the palate and the posterior hollows are shallow, and consequently much less distinct; the pterygoid fossæ are very nearly on the same plane as the palate, and are indicated only by a very slight depression. The incisor teeth are broader than in R. chinchilloides, and the molar teeth are proportionately smaller. The thin plate which forms the anterior root of the zygomatic arch is deeply emarginated in front in R. cuniculoides (see Plate 34, fig. 21, b.); but in R. chinchilloides, the anterior margin of this plate is nearly straight, (see Plate 34, fig. 20, c.)
In the form of the lower jaw of the two animals under consideration there are differences which will be more clearly understood upon comparing the figures. I will therefore merely notice one remarkable character which is found in R. cuniculoides, and that is, that the condyloid process is rather deeply concave on the inner side, a character which does not exist in R. chinchilloides, nor do I recollect having observed it in any other Rodent.
The principal dimensions of the skull of R. chinchilloides, are as follows:—
| In. | Lines. | ||
|---|---|---|---|
| Total | length | 1 | 2 |
| Width | 0 | 8½ | |
| Length | of nasal bones | 0 | 6⅓ |
| of incisive foramina | 0 | 4 | |
| Distance between the outer surface of the incisors and the first molar tooth, upper jaw | 0 | 4½ | |
| Longitudinal extent of the three molars of the upper jaw, taken together | 0 | 2¾ | |
| Length | of a ramus of the lower jaw without the incisor | 0 | 8 |
General Observations upon the foregoing Species of Muridæ.