Part 20

The specific name nasutus has been applied to this mouse on account of its elongated and slender muzzle, the tip of which extends nearly 4 lines beyond the upper pair of incisors: the rudimentary toe of the fore foot, instead of having the usual rounded nail, has a short pointed claw. Its fur is not so soft, nor yet so long as in many of the preceding species, and there is a greater admixture of yellow in its colouring. The claws appear to be adapted to burrowing.

The skull (which is not quite perfect) is figured in Plate 33, fig. 7, a, its length is 1 in. 3 lines. Fig. 7, b, represents the molars of the upper jaw, and fig. 7, c, those of the under jaw. The lower jaw, which is of a very slender and elongated form, is figured in Plate 34, fig. 10, a.

“Was caught in a small thicket on an open grassy plain, by a trap baited with a piece of bird. This mouse when alive possesses a marked character in the extreme acumination of its nose.”—D.

20. MUS TUMIDUS. PLATE XVIII.

Mus tumidus, Waterh., Proceedings of the Zoological Society of London for February 1837, p. 15.

M. brunneus, nigro lavatus; rostro ad apicem, labiis, mento, gulâ, pectore, abdomineque albis; naso suprà nigrescente; auribus mediocribus rotundatis; corpore crasso; caudâ capite corporeque breviore, pilis nigricantibus, subtùs albescentibus prope basin, vestitâ; artubus pedibusque grisescentibus; vellere longo, molli; unguibus longis.

DESCRIPTION.—Body stout; head large; tail nearly as long as the head and body; inner toe of the fore foot with a distinct, pointed claw; claws rather large, those of the fore feet but slightly arched. Fur rather long, and moderately soft; general tint of the upper parts of the body, brown, of the sides of the head and body, grayish, but with a yellow wash; the lower part of the sides of the body and of the cheeks, the tip of the muzzle, and the whole of the under parts, white; feet dirty white; ears densely clothed with short hairs, those on the inner side chiefly of an ashy-brown colour, and those on the outer side dusky; the hairs of the back are of a deep lead colour at the base, black at the tip, and annulated with yellow near the tip; the longer hairs, which are thickly interspersed, are totally black; on the under parts of the body the hairs are gray at the base, and broadly tipped with white; the upper surface of the muzzle is blackish; the moustaches are black; the incisors are yellow.

In. Lines. Length from nose to the root of tail 6 9 of tail 5 4 from nose to ears 1 8 of tarsus (claws included) 1 6 of ear 0 7

Habitat, Maldonado, La Plata (June.)

This species is about the size of Mus Rattus, but is stouter in its proportions; as in Mus nasutus, the thumb is furnished with a pointed claw. The molars of the lower jaw are figured in Plate 34, fig. 11, a.

“This rat was caught in so wet a place amongst the flags bordering a lake, that it must certainly be partly aquatic in its habits.”—D.

21. MUS BRAZILIENSIS. PLATE XIX.

Rat du Brézil, Geoff.

M. suprà fuscus fulvo lavatus; lateribus capitis corporisque æquè ac abdomine auratis; gulâ pectoreque albis; pedibus pilis sordidè flavis tectis; auribus parvulis; caudâ caput corpusque ferè æquante; vellere longo, molli.

DESCRIPTION.—Head somewhat arched, and rather short; ears small; tail about equal in length to the head and body, measured in a straight line; tarsi large. Fur long, and rather soft; general colour deep golden yellow: on the upper surface of the head and the back, long glossy black hairs are thickly interspersed, and produce, with the admixture of the deep golden colour of the ordinary fur, a dark brown tint; chin, throat, chest, and rump, white; the hairs covering the upper surface of the feet are of a dirty yellowish white colour, and on the toes nearly white: ears densely clothed with longish hairs, those on the inner side chiefly of a deep golden colour, and those on the outer side brownish; the ears are partially hidden by the long fur of the head; tail sparingly clothed with hairs, above brown, and beneath brownish-white: the fur of the back is of a deep gray colour at the base, annulated with deep golden yellow near the apex, and blackish at the apex; the longer hairs are black; the hairs of the belly are pale gray at the base, and broadly tipped with golden yellow colour; the white hairs on the throat, chest, and rump are of an uniform colour—not tinted with gray at the root;—the hairs of the moustaches are black: the incisors of the upper jaw are of a deep orange colour, and those of the lower jaw are yellow: the thumb nail is truncated.

In. Lines. Length from nose to root of tail 8 6 of tail 7 9 from nose to ear 1 8 of tarsus 2 0 of ear 0 6½

Habitat, Bahia Blanca, (September.)

This species is nearly equal in size to the common rat (Mus decumanus). Of its skull I possess but the anterior portion (see Pl. 33. fig. 3, a. and 3, b.): it appears to have been about the same size as that of M. decumanus, its proportions, however, are different: the nasal portion is broader and shorter, the ant-orbital outlet is rather smaller; the plate, forming the anterior root of the zygomatic arch, and which protects this outlet, has its anterior edge distinctly emarginated, and not nearly straight as in M. decumanus,—the zygomatic arch is stouter, the space between the orbits is narrower, the palate is more contracted, the incisors are much broader, less deep from front to back, and have the anterior surface more convex; the molar teeth are larger; the lower jaw (see Plate 34. fig. 12, a.) when compared with that of Mus decumanus also offers many points of dissimilarity; the principal differences consist in its greater strength, the comparatively large size and breadth of the articular surface of the condyles, the upright position of the coronoid process—a perpendicular line dropt from the apex of which would touch the posterior part of the last molar—and the great extent of the symphysis menti. In the form of the incisors, the more contracted palate, the great extent of the symphysis menti, and in fact in most of the points of dissimilarity, between the skull of the present animal and that of Mus decumanus, here pointed out, it will be perceived, there is an approach made to the Arvicolidæ.

The dimensions of the skull (so far as an imperfect specimen will allow of their being taken) are as follows:—

In. Lines. Distance between front of incisors, (upper jaw) and the first molar tooth 0 8 Longitudinal extent of the three molars on either side, taken together 0 4¼ Length of nasal bones 0 7¼ —— of incisive foramina 0 4¼ Width between orbits 0 2½ Length of ramus of lower jaw 1 1¼

Fig. 3, c, Plate 33, represents the molar teeth of the upper jaw. Fig. 3, d, those of the upper jaw.

“This rat was caught at Bahia Blanca where the plains of Patagonia begin to blend into the more fertile region of the Pampas. It lived in holes amongst the tussocks of rushes, on the borders of a small, still, brook; in its manner of diving and aquatic habits it closely resembled the English water-rat, (Arvicola amphibia.)”—D.

When at Paris I examined what I believe to be the original Mus Braziliensis, since the specimen was labelled “Rat de Brazil St. Hilaire, 1818.” It agrees perfectly with the present animal excepting in being rather smaller, the length from the nose to the tail being 7 inches and 4 lines—the length of the tail is 7 inches 9 lines, and that of the tarsus is 1 inch 11 lines; this difference in the length of the body may arise from difference of age, or even of sex. In the Paris Museum I saw what appeared to me to be a variety of the same species in which the under parts of the body are white.

I have been minute in my description of the Mus Braziliensis, since it is confounded by Desmarest, Fischer and Lesson with the Rat troisieme or Rat Angouya of Azara, which I believe to be a very different animal. The description given by the authors just mentioned are taken from Azara, who gives the following characters to distinguish the Rat Angouya: “Du museau à la queue, et sur les côtés du corps tout est brun-cannelle, parceque les poils ont une petite pointe cannelle; puis, ils sont obscurs et enfin blanc vers las peau. Toute la partie inférieure de l’animal est blanchâtre, plus claire sous la tête, et plus foncée entre les jambes de devant; le pelage est doux, très-serr, et le poil, qui est à la racine de l’oreille, cache le conduit de celle-ci.”

In. Lines. Length from nose to root of tail (English measure) 6 0 of tail 6 6½ of ears 0 9¾ of tarsus (the claws included) 1 3¼

It appears from this description that the Mus Angouya is a smaller animal, and differs both in colouring and proportions from the Mus Braziliensis. Brandt has figured and described a rat under the name of Mus Angouya, which in many respects agrees better with Azara’s description; there are, however, discrepancies in the dimensions.

22. MUS MICROPUS. PLATE XX.

Mus micropus, Waterh., Proceedings of the Zoological Society of London for February 1837, p. 17.