﻿76 



NORTH AMERICAN FAUNA. 



[No. 12. 



to examine; and hence the dentinal portion of the anterior prism is more ^Yidely 

 conllnent with the second inner and outer prisms; it is, in fact, an exaggeration of 

 the form indicated hy Blasins, iig. 186 (Siiugethiere DeiitschLmds, p. 345). The second 

 molar has three inner and three outer angles alternating. The third molar has like- 

 wise three inner and three outer angles, hut the alternation of the prisms is so slight 

 that the opposing inner and outer prisms are coniluent. * * ^ I am not acquainted 

 with any specimen which shows the three upper molars in place, hut Mr. Savin has 

 two specimens which retain the first and second upper grinders (fig. 1), and Mr. 

 Reid has ohtained several isolated specimens of last upper molars. The anterior 

 upper molar (fig. la) has three inner and three outer angles alternating; the second 

 tooth has three outer and two inner angles alternating. The third upper molars 

 vary somewhat; in some only three inner and three outer angles can he counted 

 (lig. 2a), while others have three inner and four outer angles. The widely- confluent 

 character of the front prisms of the lower anterior molar is repeated in these hinder 

 upper ones. It will he noticed that in all Blasius's figures of the last upper teeth 

 (I.e., p. 345) the anterior inner fold (cement space) and the two anterior outer 

 folds extend across the teeth and meet the enamel of the opposite side, while in 

 one case (fig. 190) the two inner folds pass across. Now, in most of the teeth under 

 consideration it is only the one anterior inner and one anterior outer fold which pass 

 across; in some instances the second outer fold passes farther inward, but I do not 

 think that in any instance it touches the opposite side. 



The teeth of 'ArvicoW intermedius differ in numerous characters 

 from those of Fiber, Evotomys^ and F]ieuacomys, the only known hving 



microtines with rooted mohirs. The small 

 size of the remains and the simj^le struc- 

 ture of the first lower molar are sufficient 

 to indicate that the animal is not closely 

 related to Fiber, although the charac^terof 

 the roots of the molars, as shown in figs. 



Tig. 40.-Enamel pattern of molar teeth, 5 a ^^^^l 7 pj^ XIII, is StrOUo-Jy SUffgCSt- 



Arvicola intennedias. From !N"ewton. . ~ , 



ive of this genus. The figure of the inner 

 side of the h)wer jaw (PI. XIII, fig. 3«) suggests that the posterior molar 

 is strongly displaced by the shaft of the incisor, as in Microtm. This 

 character alone would show that the species is neither an Evotomys nor 

 a FJienacoinys ; but the peculiarities of the enamel pattern furnish addi- 

 tional reasons for its exclusion from these genera. The enamel pattern 

 (fig. 40) is, as Mr. Newton remarks, almost exactly like that of Microtus 

 terrestris (see fig. 34:). It thus lacks the deep reentrant angles on the 

 inner side of the lower molars characteristic of Phenacomys, and the 

 rounded salient angles and opposite triangles characteristic of Fvo- 

 iomys. The last lower molar in particular is noticeably difi'erent from 

 that of either Evoiomys or Fhenacomys. ^Arvicola ' intermedius is appar- 

 ently still further removed from Evoiomys by the large size of the teeth 

 as compared with the jaw. There can be little doubt that the animal 

 represents a genus distinct from any now living.^ In the absence of 

 specimens, however, nothing would be gained b}^ an attempt to name 

 and define the group. 



1 Whether the rooted microtine teeth mentioned hy Nehring (Naturuisseuschaftliche 

 Wochenschrift, Nr. 28, July 1894) and hy Forsyth Major (Atti Soc. Ital. Sci. Nat., 

 XV, p. 389) helong to animals congeneric with Arvicola intermedius is purely a matter 

 of conjecture. 



