42 
ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 
Length from nose to root of tail 
of tail 
from nose to ear 
In. Lines. 
. 3 7 Length of tarsus 
. 3 9 of ear 
. 1 0 
Habitat, Bahia Blanca, ( September .) 
In. Lines. 
. 0 10 
. 0 6 
Upon comparing the skull (PI. 34, fig. 2, a .) of M. elegans with that of M. 
Musculus , the most evident points of distinction consist in the greater proportionate 
length of the nasal and frontal bones, and the slenderness of the zygomatic arch 
in the former animal. Length of skull 11 lines, width 6 lines, distance between 
front molar and outer side of incisors of upper jaw 3| lines, length of nasal 
bones 4§ lines. 
The dentition is figured in PI. 34, figs. 2. b, and 2. c. 
“ Whilst bivouacking one night on shore, amongst some sand hillocks, this 
mouse, with its tail singed, leapt out of a bush which was placed on the fire. Its 
hind legs appeared long in proportion to the front, and it did not appear to be 
very active in endeavouring to make its escape.” — D. 
Mus elegans is about equal in size to M. Musculus; the head is larger in 
proportion than in the latter, the ears are slightly larger, the tail is longer, and 
so are the tarsi. The large ears, long tail, and comparatively large size of the 
feet, combined with the greater size of the animal itself, will render it easy to 
distinguish this species from M. gracilipes and M. bimaculatus. From the last 
mentioned animal it moreover differs in having the head larger in proportion, 
the fur longer, and the colouring of the upper parts of the body somewhat darker. 
The white fur is almost confined to the under parts of the body, and there is but 
a small tuft of white hairs behind the ears, whereas in M. bimaculatus, the white 
fur extends considerably on the sides of the body, the outer side of the limbs are 
white, and there is a large and conspicuous white spot behind each ear. 
In M. elegans the whole sole of the tarsus and the carpal tubercles are 
covered with hair. In Mus bimaculatus the hinder half of the tarsus only is 
covered with hair, and in M. gracilipes both the hinder half is covered, and there 
are some scattered hairs extending almost to the two tubercles, which are situated 
at the base of the longer toes. 
The genus Eligmodontia of M. F. Cuvier, founded upon a species of mouse 
frOm Buenos Ayres, possesses nearly the same characters as the subgenus 
Calomys, established by me in the Proceedings of the Zoological Society for 
February 1837, and which included the animal above described, and two other 
species {M. bimaculatus and M. gracilipes ). M. Cuvier’s genus is distinguished 
by there being only one large tubercle on the under side of the tarsus, and in 
having the carpal pad covered with hair as well as the pad of the tarsus. In 
