“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 these characters our present animal agrees, as it does also in size and in the relative proportions of the tail and tarsus, circumstances which induce me to believe they are identical. In _M. bimaculatus_ and _M. gracilipes_ there are six naked tubercles on the under side of the tarsus, and the carpal pad is also naked. In having, however, the tarsus hairy beneath,[20] in dentition and in colouring, they agree so closely with _M. elegans_ that I think they cannot be separated generically. MUS BIMACULATUS. PLATE XII. Mus bimaculatus, _Waterh._, Proceedings of the Zoological Society of London for February 1837, p. 18.