MURID.E— AKVICOLISL*;— CUNICULUS. 245 



of the molars is totally different. In this latter respect, Cuniculus stands quite 

 alone, for it differs as much from Arvicola as from Myodes. There is little 

 occasion to enlarge upon the molar characters above given, but some further 

 general remarks may not be out of place. In Cuniculus, the lateral saliencies 

 are all sharp, the lateral triangles being long and narrow, and the median 

 zigzag line of enamel runs nearly along the middle line; this is nearly as in 

 ordinary Arvicola; while in Myodes one or the other (the external in the under 

 jaw, the internal in the upper) of the series of saliencies are obtuse, and the 

 median zigzag, besides being unusually tortuous, runs nearer one side of the 

 molar series than the other. An increase of the number of triangles of all the 

 teeth occurs. Thus, in American Arvicola the front lower molar has at most 

 three internal and two or three external lateral triangles, and Myodes has but 

 two internal and one external; here in Cuniculus there are four internal and 

 three external, making, with the anterior trefoil and posterior loop, altogether 

 six internal saliencies and five external ones. The back upper molar of 

 Cuniculus is nothing at all like Myodes; in the latter, we have four loops, all 

 transverse, one after the other, while in Cuniculus there is an anterior loop 

 and a posterior trefoil (as in Pedomys, Pitymys, &c.), separated by two external 

 and two internal lateral triangles, alternating with each other. The anterior 

 upper molar, the most constant tooth throughout Arvicola, and even in 

 Myodes scarcely differing from Arvicola, here is unique in possession of 

 seven prisms; the two additional ones to the five of Arvicola and Myodes being 

 another internal lateral one, and after this a small supplementary postero- 

 external loop. Similarly, the middle upper molar adds to the four or four and 

 a half of Arvicola and Myodes an extra internal lateral one and a small sup- 

 plementary external loop. Of the front upper molar of Cuniculus, the first 

 lateral triangle is an interior one; of the second upper molar, the first lateral 

 triangle is an exterior one. The middle and back under molars of Cuniculus 

 are correspondingly more complicated, having five or five and a half prisms, 

 the lateral of which alternate with each other; of the front under molar, the 

 first lateral triangle is an interior one; the back lower molar is a little nar- 

 rower than the antecedent one. In the upper molar series, altogether, there 

 are twelve external salient, points and eleven internal salient points; in the 

 under-molar series, altogether, there are twelve internal salient points and 

 eleven external salient points. But however minute we may thus make our 

 account of the dentition of Cuniculus as differentiated from that of either 



