MURIDA—ARVICOLINZ—CUNICULUS. 245 
a 
of the molars is totally different. In this latter respect, Cumiculus 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 Cunicudus 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 Cunicudus as differentiated from that of either 
