708 DR. C. I. FORSYTH MAJOR ON TUE [Juiie 1, 



viz. 4 and 6, 5 and 7, are opposed to each other in a similar way 

 as in Hesperomyince ; the oblique position of the rows is brought 

 about by the different connections. The third, posterior, row, 

 which remains essentially limited to the outer part of the posterior 

 margin, shows on unworn teeth of both species, more distinctly in 

 B. betsileoensis, its composition of two parts : an anterior some- 

 what stronger cusp, 5, and a posterior smaller one, 3 ; exactly as 

 in the less reduced teeth of HesperomyincF \ 



The lower molars agree with the upper ones, if we take into 

 account that they are, of course, reversed. The anterior trans- 

 verse row, restricted to the inner part, consists, as seen in unworn 

 teeth of Braclnjuromys leisileoensis (Plate XXXIX. fig. 7 i), of 

 Winge's 1 and 4. The middle row consists internally of 2 and 5, 

 which very soon become fused with the outer cusp 6. The 

 posterior ridge is composed of 3 and 7. 



To sum up. The five transverse ridges of Trechomys, e. g.^, or of 

 the Dipodide Zaptis, are in Brachyuromys reduced to three, by 

 the atrophy of 2 and 3 and their fusion with 4 and 5. 



Comparison of the Molars of the "Ehizomyes" (Tachyoryctes, 

 lihizomys) with those of Brachyuromys. 



It has been formerly stated that the molars of Brachyuromys 

 ramirohitra are almost identical with those of the African Tachy- 

 oryctes ^. There is, however, a greater difference in vertical 

 extension between the molars of the two genera than appears from 

 my former statement : those of B. ramirohitra are semi-hypselo- 

 dont, whereas the very hypselodont molars of Tachyoryctes are on 

 their way to become rootless. In lihizomys the molars are less 

 hypselodont than those of Tachyoryctes and somewhat more compli- 

 cated than in both Tachyoryctes and Brachyuromys. 



This is particularly apparent in the molars of the upper jaw. 

 "While in the latter genus we have seen the upper molars to be 

 composed essentially of three outer cusps (3 -|- 5 ; 2-|-4; 1), sepa- 

 rated by two external folds, there are four cusps in RMzomys and 

 accordingly three folds, w hich later on become three enamel islets. 

 In Rh. badius the teeth, although as complicated in an unworn 

 condition as those of the other species, become when worn more 

 similar to the unworn teeth of Tachyoryctes and Brachyuromys, a 

 fusion taking place in the anterior part of the crown. Moreover, the 

 gradual disappearance of the islets from the crown proceeds at a 

 quicker rate than in the other species of lihizomys. 



In Tachyoryctes, m. 1 sup. of young specimens has a similar struc- 

 ture to that of all three molars of lihizomys. But this complication 

 too disappears very soon, so that somewhat worn anterior molars of 



^ E. Hensel, " Beitrage z. Kennt. Saugetli. Siid-Brasiliens," Phys. Abh. k. 

 Akad. d. Wiss. Berlin, 1873, pi. i. figs. 24 a, 25 a ; pi. ii. Igs. 26 a, 28 a; pi. iii. 

 fig. 30 a. — Winge, ' Gnavere I'ra Lagoa Santa, etc.,' pi. iii. figs. I a, ID a, 12 a.-- 

 It is also apparent in several Muridaj, e. g. JJromys, Conilnrus (young), 

 ChiruTomys. 



- Winge, ' Gnavere fra Lagoa Santa,' p. llfi. 



= P. Z. S. 1896, p. 979. 



