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Show 1897.] MALAGASY GENUS BRACHYUROMVS. 717 known of Muridae, as Cricetodon and Cricetus,, would point to the opposite assumption " \ These two genera are considered by Winge to be amongst the lowest of Muridae, on account of the greater agreement in size of their m.l and m.2; m.l being more elongate in the Murince2. To these views of Winge I have to object!-(1) The molars of some of the species of Cricetodon show the transverse ridge in question. Winge refers3 to the figures of Cricetodon given by Gervais 4, who figured worn teeth. With regard to the Tertiary Muridae comprised under this generic denomination, the case stands thus:- In the older forms, e. g. Cricetodon cadurcense, Schloss.5, from the Quercy, not only the middle transverse ridge, ending in 2, but also 1 and 3 are present, as they are likewise present in Eumys 6 (which does not seem to differ much from Cricetodon, both being very similar to the less simple molars of many Hesperomyince). Besides, we find in Cricetodon cadurcense a primitive feature of m. 1 which is almost identical with m. 2. In the more recent species of Cricetodon, from the Middle Miocene of Steinheim and La drive Saint-Alban, I observe a greater approach to Cricetus; m. 1 is larger and more complicated as compared with m. 2, and the accessory crests of all the molars tend to disappear. (2) In the Malagasy Muridae the difference in size between m.l and m.2 is even less, and their agreement in form greater than in Cricetus, Cricetodon, and the Hesperomyince, which is one of my reasons for regarding them as more primitive Muridae than the above-named. And still we have found 1, 2, and 3 to be present in molars of young Brachyuromys betsileoensis. In other Malagasy Muridae, to be described on a future occasion (Nesomys, Gymnuromys, Brachytarsomys), they are still more evident, and not in the least limited to young stages 7. (3) In the Tertiary such simple forms of molars as exhibited by Mystromys, Cricetus, " Hesper. expulsus" and " Habrothrlx laslurus" are not known. Tbe latter two, apart from tbe pattern of their molars, agree in all the rest with the other Hesperomyince (having more complicated molars) than with Cricetus. The latter genus is apparently derived from some such form as Cricetodon by a greater reduction of its molars, just as the Hesperomyince, with simpler constructed molars, appear to be derived from those with more complicated teeth. With reference to its teeth I have therefore recently called Cricetus a terminal form amongst Muridae8. Winge bas, in this conjunction, urged the similarity of the m.2 of Cricetus with other Mammalia 9. I know of no greater agree- 1 ' Gnavere fra Lagoa Santa,' p. 11; and footnote 6, p. 151. 2 " O m grieske Pattedyr," Meddel. Naturh. Foren. i. Kjobenhavn, 1881; ' Gnavere fra Lagoa Santa,' pp. 123, 124. 3 " O m graske Pattedyr," I. c. p. 22. 4 Zool. Pal. franc, pl. 46. fig. 3. 5 L. c. pl. xii. (viii.) figs. 28, 35. 6 Leidy. 7 In the same way the Dipodine Zapus, in which m.l and m.2 are of absolutely the same conformation and size, shows likewise 1, 2, and 3 well developed. 8 P. Z. S. London, 1896, p. 980. 9 Meddel. Naturh. Foren. 1881, p. 26; ' Gnavere fra Lagoa Santa,' p. 11. PROC ZOOL. Soc-1897, No. XLVII. 47 |