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Show "Jl DR. 0. I. FORSYTH MAJOR ON THE [June 1, cusps forwardsl. The small cusps outside from the large " outer " cusps he supposes to be a new addition iu Murince 2. Now, it is possible to show with the help of the Nesomylnce (1) that'these supposed new additions of Murlnce are the homologues of the outer cusps 4 and 5 of Hesperomyince and Nesomylnce, which in Murince atrophy to a certain extent as compared with the two former groups. And (2) that those cusps which in Murince Winge considers to be 4 and 5 are in reality the intermediate cusps, which in this subfamily have acquired a considerable size 3. As regards the anterior upper molar (m. 1) in Murlnce, the anterior side of this tooth is tripartite, whereas it is bipartite in Hesperomyince, which last present three internal cusps against two in the former subfamily4. The clue for an understanding of tbe homologies is afforded by some of the Nesomyince, by young Brachyuromys betsileoensis (Pl. X X X I X . fig. 7 a), and more than all by Nesomys (text-figure 3). The comparison with Nesomys shows that the middle part of the tripartite anterior side of the Murine m. 1 is an intermediate cusp strongly developed ; the outer part is cusp 1, more developed than in in. 2 ; the internal 1 Vidensk. Meddel. fra d. Naturh. Foren. i Kjobenhavn for Aaret 1881, Kjobenhavn, 1882, p. 27. - L. c. p. 27: " idet bver af dem " (i. e. ydre Knolde), " paa sin Yderside af-sajtter en lille Knold, der dog ikke er skilt fra Moderknolden." 3 Some years ago Prof. Osborn arrived at the conclusion that these median cusps in the upper molars of Mus are homologous with tbe " intermediate " cusps in other Placentals (H. F. Osborn, " The Rise of the Mammalia in North America," I. c. p. 19). H e considers this to be a victorious argument against m y own views, being, according to what he states (/. c. p. 18), an " evidence that the multitubercular molar instead of being primitive was derived from the tritubercular " ; and farther on (p. 19), that " the molars of the mouse (Mus), and of certain kangaroo-rats (Dipodoynys and Perognathus), illustrate beautifully tbe recent stages between trituberculy and multituberculy, showing that the intermediate tubercles of Mus (also common in other Placentals) give rise to the intermediate or third multituberculate row." However, in such of the Murida? in which these " intermediate " cusps are somewhat less developed (e. g. Nesomys), or more or less suppi-essed (e. g. several Hesperomyince, Cricetus, Mystromys), we do not for that reason find a nearer approach to tritubercular forms. I a m quite prepared to concede to Prof. Osborn that, some of the features common to the molars of Allotheria and of Murince may have been independently acquired in each. One might even suggest that the wbole of the outer series of cusps in tbe upper molars of Allotheria are tbe homologues of the outer series 1, 2, 3 of Winge, and, as a consequence, that the second range in the Allotheria corresponds to 4, 5 of Winge (paracone and metacone of Osborn); in that case the internal range of the former would be the homologue of the intermediate cusps of more modern Mammals. It would further follow that Cope's and Osborn's protocone (Winge's 6), absent in the Allotheria, is in reality a later addition, as bas been suggested by Winge; so would also be the postero-inlernal cusp (Winge's 7), in which last assumption Winge agrees with Cope, Osborn, etc. With the materials at present available, such a supposition could be neither proved nor disproved for the moment. More to the point is, that the "intermediate" cusps of Mus are " also common in other Placentals," and especially in (geologically speaking) older forms ; and that they are present not only in the " Laramie Multituberculates," but as well in several of those molars which have been comprised by Osborn under the denomination of "Laramie Trituberculates." (Cf. pl. viii. of "Fossil Mammals of the Upper Cretaceous Beds," I. s. c.) 4 In several Murince there is an additional small postero-internal cusp, |