MAMMALIA. 



59 



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. 



Length from nose to root of tail 

 of tail 

 from nose to ear 



In. Lines. 



8 6 



7 9 



1 8 



Length of tarsus 

 of ear 



In. Lines. 

 2 

 U 



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 PI. 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 31. 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 dis- 

 similarity ; the principal differences consist in its greater strength, the com- 

 paratively 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 



* I am sorry to say the artist has not drawn this skull with his usual fidelity, a circumstance which I did not 

 perceive until it was too late to make any alteration : it is too large, and the incisors are represented as project- 

 ing forwards too much ; they are in the original so nearly at right angles with the upper surface of the skull 

 that but a very small portion of them is seen, when it is viewed, as represented at fig. 3, a. 



