MAMMALIA. 
49 
inner side are yellow at the apex and gray at the base ; on the outer side 
they are of a brownish colour, and on the fore part blackish. The hairs of 
the moustaches are short and slender, and of a brownish colour. The head 
is large. 
In. Lines. 
Length from nose to root of tail . .43 
of tail . . . . .29 
from nose to ear . . .10 
Habitat, Maldonado, La Plata, {June.) 
This species is rather larger than the common mouse ; its head is proportion- 
ately larger, the ears are smaller, the tail considerably shorter, and the fur longer, 
and in colouring it is a little darker. In size and colour it resembles M. Magella- 
nicus, but the shorter tail and tarsi, and the smaller size of the ears will serve to 
distinguish it. 
The skull of Mus arenicola, Plate 34. fig. 7, a, is rather larger than that of 
Mus Musculus, the nasal portion is broader, the interparietal bone is much 
smaller, especially in antero-posterior extent ; the zygomatic arches are more 
slender, and the incisive foramina are broader. The horizontal ramus of the lower 
jaw (PI. 34. fig. 7, d.) is rather less curved, the coronoid process is more elongated, 
and the condyloid is narrower and also larger. The length of the skull is 11 lines 
and a half; the width is 6^ lines. The molars of the upper jaw are figured in 
plate 34 fig. 7, b. and those of the under jaw, fig. 7, c. 
“ This specimen was caught on the open grassy plain, by a trap baited with 
a piece of bird ; it is, however, very abundant in the sand hillocks near the coast 
of the Plata.” — D. 
Length of tarsus (claws included) 
of ear 
In. Lines. 
0 10 
0 4i 
1 3. MUS BRACHIOTIS. 
Plate XIV. 
Mus brachiotis, Waterh ., Proceedings of the Zoological Society of London for February 1837, p. 17. 
M. supra obscurb fuscus , subtus obscurb griseo tinctus ,• pedibus griseo-fuscis ; 
auribus parvulis ; caudd quoad longitudinem, corpus ferb cequante: vellere longo 
et molli. 
Description. — Fur soft, very long, and dense ; ears very small ; general colour 
brown : the hairs of the upper parts, and sides of the head and body are of 
H 
