OCR Text |
Show 538 MR. W. L. SCLATER ON SOME INDIAN MURIDAE. [June 17, internal, one posterior cusp, and in addition has externally a slight projection which seems to represent a rudimentary external cusp. The molars of the lower jaw are even more remarkable: the anterior one consists of eight cusps arranged exactly as those of the molar of the upper jaw, but the anterior external cusp is wanting; the second lower molar consists of six cusps arranged as in the corresponding tooth above, while the posterior molar consists of four cusps only, representing the two central and two external cusps, with a slight trace of the anterior external cusp. This curious dentition, taken in conjunction with the facts abovo mentioned about the dentition of Chiropodomys, seems to lead to the inference that we have in Hapalomys a very primitive form of Eat, by which the dentition of Mus may to a certain extent be explained. The upper molars of Mus are easily derivable from a molar such as that of Hapalomys by the increase in size of the central row of cusps and the suppression of one of the lateral ones ; so, too, with Vandeleuria. In the case of the molars of the lower jaw the condition in Mus and Vandeleuria seems to be directly connected with that in Hapalomys by the intermediate condition as exhibited in Chiropodomys ; in Hapalomys the external row of cusps is already slightly inferior in development to the central and internal rows, and in the case of the anterior molar one cusp is already lost ; in Chiropodomys the outer row of cusps has been reduced to the cingulum running along the external face of the molars described above : while in Vandeleuria and Mus the outer cusps have altogether disappeared, not leaving any trace even of the cingulum, and the molar is bilaterally symmetrical. These remarks are merely suggested as a method by which a small step in the evolution of Murine molars may have taken place; it would be absurd to lay any great stress on this theory, as I have only been able to examine the skulls of Indian Rats, and I do not claim to have any acquaintance with the numerous exotic forms. The following are the measurements of the unique spirit-specimen of Hapalomys longicaudatus :-Head and body 5-^7, tail 7*9, hind foot T05, forearm and hand 1-58, ear-conch *35, muzzle to ear (skull extracted) 1-40. 1 skin. ] al. 3 al. 1 al. 8 al. 3al. List of the Types of Muridae in the Indian Museum. Names. Author. Eemarks Nesokia scullyi. Wood-Mason. Nesokia barclayanus. Anderson. Nesokia elliotanus. Anderson. Mus robustulus. Blyth. Mus sladeni. Mus yunnanensis. 2 skins. Mus ncmoralis. Anderson. Anderson. Blyth. = N. bengalensis. = N. nemorivaga. = Mus rattus rufescens. = Mus rattus rufescens. = Mus rattus rufescens. = Mus rattus rufescens. |