714 DB. C. I. FOKSYIlt MAJOU ON THE [Juue 1, 



cusps forwards \ The small cusps outside from the large "outer" 

 cusps he supposes to be a new addition iti Murince ~. Now, it is 

 possible to show with the help of the Ntsomyince (1) that these 

 supposed uew additions of Murince are the hoinologues of the 

 outer cusps 4 and 5 of Hesperomy'mce and Ncsomi/iiue, which in 

 ATurince atrophy to a certain extent as compared with the two 

 former groups. And (2) that those cusps which in Murince 

 AViuge considers to be -t and 5 are in reahty the intermediate 

 cusps, which in this subfamily have acquired a considerable size ^. 



As regards the anterior upper molar (m. 1) in Murime, the 

 anterior side of this tooth is tripartite, whereas it is bipartite 

 in Hesperomijince, which last present three internal cusps against 

 two in the former subfamily ^. The clue for an understanding 

 of the homologies is afforded by some of the Nesomi/ince, by young 

 Brachyuromi/s beisileoensis (PL XXXIX. fig. 7 a), and more than 

 all by I^esomys (text-figure 3). The comparison with Nesomys 

 shows that the middle part of the tripartite anterior side of 

 the Murine m. 1 is an mtermediate cusp strongly developed ; the 

 outer part is cusp 1, more developed than in m. 2 ; the internal 



1 Vidensk. Meddel. fra d. Naturh. Foren. i Kjobenhavn for Aaret 1881, 

 Kjobenhavii, 1882, p. 27. 



" L. c. p. 27: " idet hver af dem" (i. e. ydre Knolde), '' paa sin Yderside af- 

 sietter en lille Knold, der dog ikke er skilt fra Moderknolden." 



^ Some years ago Prof. O.sborn arrived at the conclusion that these 

 median cusps in the upper molars of Mus are homologous with the "inter- 

 mediate " cusps in other Placeutals (H. F. Osborn, " The Ei.se of the Mammalia 

 in North America," I. c. p. 19). He considers this to be a victorious argument 

 against my own views, being, according to what he states {l. 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 {Dipodomys and Perognathns), 

 illustrate beautifully the recent stages between trituberculy and multituberculy, 

 showing that the intermediate tubercles of Mus (also common in other Placeu- 

 tals) give rise to the intermediate or third multituberculate row." However, in 

 such of the Muridae in which these " intermediate " cusps are somewhat less 

 developed (e. g. Nenomys), or more or less suppressed (e. g. several Hespero- 

 myincE, Cricetus, Mystromys), we do not for that reason find a nearer approach 

 to tritubercular forms. 



I am quite prepared to concede to Prof. Osborn that some of the featm-es 

 common to the molars of AUotheria and of Murince may have been indepen- 

 dently acquired in each. One might even suggest that the whole of the outer 

 series of cusps in the upper molars of AUotheria are the homologues of the 

 outer series 1, 2, 3 of Winge, and, as a consequence, that the second range in 

 the AUotheria corresponds to 4, 5 of Winge (paracone and metacone of Osborn) ; 

 in that case the internal range of the former would be the humulogue of the 

 intermediate cusps of more modern Mammals. It would I'urther follow that 

 Cope's and Osborn's protocone (Winge's 6), absent in the AUotheria, is in 

 reality a later addition, as has been suggested by Winge ; so would also be the 

 postero-iuternal cusp (Winge's 7), iu 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," aud 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 Oaboru under 

 the denomination of "Laramie Trituberculates." {Cf. pi. viii. of "Fossil 

 Mammals of the Upper Cretaceous Eeds,'' I. s. c.) 



1 In several Muri/ice there is an additional small postero-internal cusp. 



