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Show 1888.] OF THE SOLOMON ISLANDS. 481 each other specifically, they have a great many characters in common, as for example their considerable size, the general forms of their skulls and teeth, and, notably, their very unusual mammary formula, 0-2 = 4, a formula only found, so far as I know, in two other members of the genus, namely Mus trivirgatus, Temm., and M. dehcatulus, Gould, both quite small species, and the latter nearly, if not quite, the most diminutive member of the genus. ^ It is, however, in their relation to each other that their chief interest lies, for they seem to be clearly the slightly modified descendants of one single species that, once introduced, has been isolated in Guadalcanar for some considerable time, while it has apparently died out elsewhere. Of this original species some individuals would have adopted a terrestrial, and others an arboreal life, and their respective descendants would have been modified accordingly. In this way I would explain the fact that at the present time°we have in Guadalcanar two genuine species, agreeing with each other in their essential structure, and yet separated by a considerable number of characters all having a more or less direct relation to a climbing or non-climbing habit of life. Of these, of course by far the most striking are the broad foot-pads and the long, rasp-like, probably semi-prehensile tail of Mus rex, as compared to the smaller pads and short smooth tail of Mus imperator. 20. Mus SALAMONIS, Rams. Mus salamonis, Rams. P. Linn. Soc. N. S. W . vii. p. 43 (1882). I know nothing more of this species than is contained in the original description. Its hind foot is stated to be 44 millim. in length, and its locality is Florida Island. The length of its hind foot, curiously enough, exactly fills in the gap between that of M. rex and of the next species, so that the four Solomon Island Rats have the lengths of their hind feet just in the progressive series 34, 44, 54, and 64 millim. 21. Mus PRAETOR, Thos. (Plate XXII. fig. 6.) Mus praetor, Thos. t. c. p. 158. a, b. 8 2- Aola. Size about that of Mus rattus. Fur short, mixed with numerous spines, and with a few much longer piles on the posterior back. General colour coarsely grizzled grey, the longer piles and the spines black-tipped, the ordinary fur with yellow tips; the bases of all pale slaty grey. Underside dirty white, in old specimens yellow ; the hairs all grey at base. Ears rounded, rather short, laid forward they just reach to the posterior canthus of the eye. Mammae 2-2 = 8. Hands and feet greyish white, a darker patch on the terminal part of the metatarsus. Hind feet (Plate XXII. fig. 6) rather short in proportion to the size of the animal; fifth toe reaching to the middle of the first phalanx of the fourth ; soles naked, the pads rounded, rather small. Tail short, not so long as the body without the head, thinly haired and coarsely scaled, the rings of scales averaging about 10 to the centimetre; its colour wholly deep black. |
