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Show 1896.] ZOOLOGICAL EXPEDITION TO MADAGASCAR. 979 uromys, Hypogeomys-Brachytarsomys stands somewhat apart from the others and requires further investigation-belong to the so-called Cricetine group of Muriform (" Muridae," auct.) Rodents, of which they are the lowest of existing forms, having affinities with some of the least specialized of the family Dipodidae, as defined by Winge, viz. to Sminthus and Zapus. The African and Asiatic Rhlzomyes, usually considered as belonging to the Spalacidae, but which the last-named author places amongst the lowest Muridae, alongside with the tertiary Cricetodon and Eomys, are nearly related to the Malagasy group of Rodents by means of the Abyssinian Tachyoryctes (Rhizomys) and the Malagasy Brachyuromys, the former being but a very specialized fossorial form of the more generalized Brachyuromys ramlrohltra. The molars are almost identical in botb, only but slightly more hypselodont in Tachyoryctes. If we divest the Tachyoryctes skull of its fossorial characters aud of the consequences of the more hypselodont molars, we obtain a Brachyuromys skull. Likewise the skulls of the young Tachyoryctes bear much greater resemblance to Brachyuromys than the adult. There is further a great correspondence in external characters if we disregard the smaller ears aud eyes of Tachyoryctes and its fossorial claws. As to the affinities of tbe Malagasy Rodents with the lower Dipodidae, they are revealed by the skull as well as by the conformation of the molars. The infraorbital foramen is large throughout and especially in Brachyuromys, though on the whole showing the form characteristic for the Muridaex, tbe posterior part of the zygomatic arch is bent downwards, the malar bone strongly developed and approaching the lachrymal more than ia any other Muridae, the size and shape of the incisive foramina nearly approaching what obtains in the Dipodidae, &c. With regard to the teeth, the group of Malagasy Rodents, together with the Abyssinian Tachyoryctes, differ in a very important condition from the more specialized Murinae, and even from the Cricetiiie Rodents, in having their molars of almost equal size and form; the two anterior molars especially are very much like each other. This likewise is a character in which they approach the lower Rodents, especially the Dipodidae; in the pattern of the molars there is equally a strong resemblance of them all with Dipodidae (Sminthus, Alactaga, Zapus); in this respect tbe mosaic pavement-like triturating surface, both in the Malagasy Gymnuromys and the Nearctic Zapus, is especially noteworthy. The relation of the Madagascar Rodents to Cricetus, which is considered to be the type of the group, is viewed by me as 1 The miocene Paciculus, from tbe John-Day beds in N. America, is considered by Scott to stand in most respects in an intermediate position between Trotoptychus (which Scott supposes to be tbe ancestral form of tbe Dipodidaj) and the Dipodidse, although it has lost all the premolars, and the lower portion of the infraorbital foramen forms, as in the Muridse, a distinct notch for the passage of the nerve. (" Protopti/chus hatcheri, a new Eodent from the Uinta Eocene," Proc. Ac. Nat, Sc. Philadelphia, 1895, p. 269.) |
