ALLEN: MAMMALIA. 



215 



internal salient angles. The second upper molar consists of three closed trans- 

 verse prisms, the outer angles of which are slightly in advance of the correspond- 

 ing angles of the inner side. The tooth has 

 three salient angles on each side. The last 

 upper molar is much like the one preceding, but 

 the posterior enamel space, which has two small 

 and opposite prisms at its anterior end, is pro- 

 duced in the long axis of the tooth into a narrow 

 heel, with nearly parallel sides. There are there- 

 fore six salient angles in this tooth as in the sec- 

 ond molar. In the specimen figured, however, 

 there are indications of a small additional pair 

 of angles, one oh the outer and one on the inner 

 side of the posterior heel, and this condition I 

 also found in a specimen of M . melanogaster. 



The first lower molar has four closed enamel 

 spaces the anteriormost with two mternal and 

 one external prominent projections; the three 

 other spaces, are formed by the confluence of 

 the prisms of opposite sides into a single trans- 

 verse space. The tooth has four external and five or even six internal salient 

 angles according as the very small antero-internal point is less or more devel- 

 oped. The second and third lower molars show each three transverse closed 

 spaces, and each has three salient angles on either face. The reentrants of the 

 third lower molar are somewhat deeper externally than in M . aurora. 



Measurements: --The type and three other specimens were measured in 

 the flesh by the collector, as follows :- 



D 



Microtus (Eothenomys) mucronatus. 

 Type No. 7790. C, Enamel pattern of 

 right upper molars. D, Enamel pat- 

 tern of right lower molars. 



The ears of the dried skins measure 11 or 12 mm. in length from the meatus. 

 which is 3 or 4 mm. greater than the corresponding dimension in skins of M, 

 melanogaster. 



The skull of the type measures: greatest length, 26; basal length, 23.8; 



1 Probably a mistake since the skin as made up is quite as large as the other specimens and measures 

 137 mm. in length. 



