716 DR. c. I. FOBsrxH MAJOE ON TUE [June 1, 



connects itself, as often in Hesperomyincf, with the postero-internal 

 cusp 5, with which it becomes fused at au early date (in another 

 Malagasy genus, Gi/ntnuromijs, it remains independent). 



Nor is the antero-interual cusp, 1+4, simple, although it is 

 undivided in Brachyuromys. In the Hesperomyince it presents 

 itself frequently as a simple cusp, but in several forms, " B. ratti- 

 cejys," ' " H. longicaudatus" '^ " //. tumidus," ^ it appears as com- 

 posed of two parts separated by an enamel islet — an anterior 

 smaller cusp (Winge's 1, Oshorn's 2>araco)iid), and a jjosterior larger 

 cusp (the antero-internal cusp, 4). In ]\"esomys the original com- 

 pound structure of this cusp (1 + 4) is likewise shown, in moderately 

 worn molars, by an enamel islet ; and in very young B. hetsileoemis 

 it is foreshadowed by a slight depression of the enamel. 



Trom this comparison of the lower molars of 2sesomys with 

 those of Brachyuromys hdsileoends and Hesperomyince, it results 

 that the molars of the former approach closer to certain forms of 

 Besperomyince in the conformation of their pattern, the latter to 

 others. The internal enamel-folds remain for a longer time open 

 on the inner side in the teeth of Brachyuromys and several 

 Besperomyince than in Nesomys. In the relative positions of outer 

 and inner cusps Brachyuromys differs from some other Hespero- 

 wyitice. In both B. beisileoensis and B. ramirohitra the postero- 

 internal cusp, 5, stands directly opposite the interspace (inlet) 

 dividing the two outer cusps (6 and 7), so that it comes to 

 alternate with the latter, as in " B. vulpinus" * B. squamipes'^ ' ; 

 in these same Hesperomyince and in Brachyuromys 3 is more 

 developed, whilst 2 is atrophied. In other Besperomyince the 

 princi])al outer and inner cusps are almost opposite each other, 

 as in JS'esomys. BracJiyuromys agrees more with " B. vulpiims^' ^ 

 and " B. arenicola ? " " (the former is somewhat hypselodont ; the 

 tig. of the latter presents a much worn molar) ; Nesomys with 

 •' B. ratticeps" ^ " B. longicaudatus,'' " " B. suhttrraneus " '". The 

 form of " B. squamipes " " agrees with both of them. 



As was pointed out above, a still more advanced atrophy of 

 1, 2, and 3 leads us to such simple forms amongst Muridae as 

 Cricetus, Alystromys, " Besperomys e.rpulsus," '^ " Bahrothrix lasi- 

 urus," " " Besp. nasuhis," '^ in which the pattern of the crown 

 shows essentially only four cusps. "Winge is doubtful whether 

 the presence or the absence of the '• transverse ridge " between 

 the outer cusps, 4, 5, in upper, and the inner cusps iu lower 

 molars is the primitive condition in Muridae ; adding, "its presence 

 in Smiiiihus, Scirteies, and several other low Eodents leads to the 

 assumption that this condition is the primitive one in Muridae ; 

 whereas the absence of this ' transverse ridge ' in the lowest 



1 Hensel, /. c. nl. i. fig. 2.5 b. '' Ih. pi. ii. fig. 28 h. * lb. pi. iii. fi?. 30 b. 



* Hensel, I. c. pi. i. fig. 23 b. ' lb. pi. i. fig. 24 b. <" lb. pi. i. fig. 23 i. 



- lb. pi. ii. fig. 27 b. " lb. pi. i. fig. 2.5 b. « lb. pi. ii. fig. 28 b. 



'" lb. pi. iii. fig. 31 *. '^ lb. pi. i. fig. 24 6. 



'^ Winge, 'Gnavere fra Lagoa Santa,' pi. ii. fig. 4 a. 



'•' Ih. pi. ii. fig. 11«. 



" Hensel, 'Beitr. KeniUu. d. Siiugeth. Siid-Bru.-i.' pi. iii. figs 19, 29. 



