﻿74 



NORTH AMERICAN FAUNA. 



[Xo. 12. 



The molars, wliich are rooted, do Dot differ essentially in enamel pat- 

 tern from those of living species of 2Iicroius^ except that the back 

 upper tooth is remarkably simple in structure, and the reentrant angles 

 in all the teeth are so shallow that the triangles are open. \Yhile the • 

 front lower molar has nine salient angles, as in typical Microtus, the pos- 

 terior maxillary tooth has only four and a very small terminal looj). 

 Tlie author remarks that the open triangles give the teeth of Bramiis a 

 resemblance to those of some of the GerhiUidcc, but this likeness must 

 be very superficial. The most remarkable character of Bramus is the 

 form of the mandible, which is like that of Castor and very unlike that 

 of any of the Murklcv. It is probable that Bram us is the type of a group 

 differing too widely from any of the recent Microtince to be united with 

 them in one subfamily. 



The subgenera IsodeUa and Anaptogonia were described by Prof. 

 E. D. Cope in 1873 (Proc. Amer. Philos. Soc, XII, p. 87). Both are 

 based on teeth from the Postpliocene deposit in Port Kennedy Cave, 

 Pennsylvania. Anaptogonia is very different from any of the living 

 subgenera of Microtus — so different that, as Professor Cope suggests, 

 it may be eventually recognized as a distinct genus. Isodelia, on the 

 other hand, is hardly separable from Pitymys, since the characters 

 pointed out as diagnostic of the two groups are not beyond the range 

 of variation among the species of one subgenus. 



The original description of Microtus hiatidens, the type of the suh- 

 gemis, Anaptogouia, is as follows: 



Represeuted by several molar teeth. These are several times as large as the teeth 

 occnpyiug the same position in any of the species already mentioned in this essay, 

 and suggest the genus Fiber. The distinctive features of the latter are the com- 

 pressed, oar-like tail, vrith rooted molars, and it is evident that the relationship of 

 this species is not to it. Perhaps it is neither an Aricola (sic.) l = 2Iicrotus'] nor a 

 Fiber, since it differs in the structure of the teeth from the known species of both. 

 None of the triangles are isolated, but are connected by a narrow strip of dentine, 

 which is narrow posteriorly, but widens anteriorly until it opens out into the ter- 

 minal loop. Thus the sectional name Anapiogonia may be found ultimately appli- 

 cable to a separate genus. The separation of the enamel folds merely carries to the 

 hig-liest degree that which is seen in the anterior part of the tooth of ^. sigmodas. 



In the inferior m 1 the triangles, which do not open on one side to the anterior 

 loop, are 1^, then one on each side, and the short, wide, terminal loop, which is 

 bilobed or emarginate in the middle of the end. The ridges, which are very promi- 

 nent and acute, are, therefore, f ; at the extremity there are two short ones, between 



mais elles sont de bonne heure parfaitement distinctes I'uue de I'autre. La troisieme 

 molaire iuferieure, un pen plus arquee que dans ArvicoJa, ne descend pas a la face 

 interne de I'incisive, mais reste tout a fait au-dessus, et ses racines seules s'insinueut 

 un XDCU lat^ralement sur cette face. 



L'os mandibulaire presente des differences beaucoup plus importantes. Son 

 apoj)hyse angulaire, restaiit presque dans le plan general de I'os, ne fait en arriere 

 qu'une l^gere saillie bordant la branche montante, qu'elle suit tres haut sous le 

 condyle pour se terminer en simple ijetit cran. II y a une grande analogic de forme 

 avee ce que I'on voit chez les Castors. Dans Arvicola, au contraire, Tapophyse 

 angulaire est basse et se rejette obliquement en arriere en forme de cuilleron forte- 

 ment crochu et tordu, rajjpelant du reste, sauf cette torsion la disposition de cette 

 partie chez les autres Murides. 



