1897.] MALAGASY GENUS BEACHTUEOMYS. 715 



part is the autero-internal cusp 6, which, together with 7, appears 

 always shifted forwards in Murince, as was assumed by Wiuge '. 

 In HesperomyincB cusp 6 stands opposite the outer cusp 4 ; it is 

 the median of the three internal cusps of m.l ; the anterior one 

 is the homologue of the intermediate cusp, above mentioned, of 

 Murines, which in Uesperomyince occupies a more internal position. 

 In Nesomys (text-fig. 3) this intermediate cusp occupies the same 

 position as in Murince, but it is much less developed than either 

 in Muriiice or in Hesperomyince ^. Owing to the smaller size of 

 this cusp and to its position on the anterior side of the tooth, 

 the formation of an anterior fold, i. e. " interspace," between this 

 intermediate cusp anteriorly and cusp 6 posteriorly, which we 

 have in Uesperomyince, is not arrived at in Nesomyince. The 

 antero-internal cusp, 6, occupies in the latter about the same 

 position as in the former ; it is much less shifted forwards than 

 in Murince. 



Lower Molars of Nesomys. — With regard to the lower molars in 

 Hesperomylme and Nesomys, there can be no doubt as to which are 

 the two principal internal cusps. The posterior internal cusp, 3, 

 is sometimes rather strongly developed in Hesperomyince, just as 

 in Brachyuromys ; in other members of the group it is reduced as 

 compared with 4 and 5, just as in Nesomys. In the HesperomyincB 

 the median crest, corresponding to 2, either remains rather 

 independent, reaching the inner side, but still with the tendency 

 to cling to the antero-internal cusp : or it is more or less 

 intimately connected with the postero-interual cusp, 5. In the 

 latter case we find an enamel islet as remainder of the original 

 separation ^. In Nesomys the median crest becomes fused, near the 

 inner side, with the posterior part of the antero-internal cusp, 4 ; 

 a configuration to which there is an approach in those Hespero- 

 myince, " If. ratticeps," * " M. lonyicaudatus," ' " H. 7iasutus," " 

 H. subterraneus," '' in which the usually independent crest leans 

 against the antero-internal cusp. 



In both Hesperoviyince and Nesomys the principal outer cusps, 

 6 and 7, are internally connected by a small longitudinal crest, 

 from which the median transverse crest, 2, starts inwards at right 

 angles. In Brachyuromys hetsileoensis the aforesaid small longi- 

 tudinal crest is likewise present, which explains the formation in 

 this species of two creeks, an outer and an inner one, corresponding 

 to the transverse valley in B. ramiroMtra. In unworn teeth of 

 Br. hetsileoensis the median transverse ridge, 2, starting at right 

 angles from the longitudinal crest, is equally to be seen ; it 



1 Considering the backward inclination of the intermediate and external 

 cusps of MuriiifS, whilst tlie inner cusps remain upright, it might be questioned 

 whether the latter have shifted their place forwards, or not rather the former 

 backwards. 



^ This is one of the reasons for the great similarity between m.l and m.2 in 

 this as well as in the other Murines, as compared to what we find in the two 

 subfamilies just mentioned. 



^ See the figures in Hensel, l. c. 



* Hensel, I.e. pi. i. fig. 26 6. ^ Jb. pi. ii. fig. 286. 



^ lb. pL iii. fig. 296. ? lb. pi. iii. fig. 31 b. 



