Of this species, there are six specimens in Mr. Darwin’s collection; two were found “living in the short grass, near the summit of the Island of Ascension, where the climate is temperate.”—D. Two others were procured “on a small, stony, and arid island, near Porto Praya, the capital of St. Jago, in the Cape de Verde Islands,—climate very hot and dry. Excepting during the rainy season, which is of short duration, these little animals can never taste fresh water, nor does the island afford any succulent plant.”—D. A specimen was also procured “on a grassy cliff, on East Falkland Island, at the distance of a mile from any habitation. It is singular that so delicate an animal should be able to subsist under the cold, and extremely humid climate, of the Falkland Islands, and on its unproductive soil.”—D. These specimens are all of them rather less than full grown individuals of the same species procured in England; in other respects, they do not differ. The sixth specimen, which is from Maldonado, is considerably less than British specimens of the common mouse, and is of a richer and brighter colour, the head is smaller, the muzzle shorter in proportion, whilst the tarsi are even longer than in a large specimen of _M. Musculus_. These points of dissimilarity induced me to believe it was a distinct species, and to apply to it the specific name of _brevirostris_.[17] Upon re-examination, with the advantage of more experience, and consequently a better knowledge of the characters of these animals, I have changed my opinion. The teeth indicate that it is not an adult specimen, and agree perfectly with those of _M. Musculus_, both in form and size. “Common in the houses of the town of Maldonado, and its habits are similar to those of _Mus Musculus_.”—D. 6. MUS LONGICAUDATUS. PLATE XI. Mus longicaudatus, _Bennett_, Proceedings of the Committee of Science and Correspondence of the Zoological Society of London for January, 1832, p. 2. _M. pallidè flavescenti-fuscus; corpore subtùs albo, levitèr flavo lavato; pedibus albis; tarsis permagnis; caudâ perlongâ; auribus parvulis._