64 BULLETIN 144, UNITED STATES NATIONAL MUSEUM 



three-fourths the distance to the elbow. The paler tips of the dorsal 

 hairs are shorter and less glossy than those of Myotis lucifugus^ with 

 the result that M. yvmumensis usually appears very dull colored in 

 contrast to M. lucifugus with its deeper, more glossy fur. It is ordi- 

 narily possible to separate out the two species in a mixed series by 

 recourse to this character alone. 



Skull. — The skull, as compared with that of Myotis lucifugus, is 

 not only smaller in size (total length 13,2 to 14.2 mm. instead of 14.0 

 to 15.8 mm.) but different in proportions. When the skull is viewed 

 in lateral profile the alveolar line appears to rise from behind for- 

 ward at a more abrupt angle, the forehead seems more pronounced 

 and higher, so that the rostrum is separated from the brain case by a 

 more obvious concavity, and the occiput is relatively more elevated. 

 The entire brain case as seen from above has a more distinctly globu- 

 lar aspect. The temporal ridges, even in adults, are barely discern- 

 ible, but sometimes they unite to form a low crest. This crest is so 

 rarely developed that we have found it in only 9 of 70 adult skulls. 

 Even when obvious the crest is noticeably flat-topped and much 

 broader than high, while that of M. lucifugus, posteriorly at least, 

 is of the usual narrowly ridgelike form if developed at all. The 

 posterior outline of the occiput when viewed from above is distinctly 

 more abrupt in its curvature than that of M. lucifugus. All these 

 differences are, in such small objects, very minute and at first some- 

 times difficult to appreciate, but they are, nevertheless, striking when 

 carefully studied. 



Teeth. — The teeth resemble in general those of Myotis lucifugus. 

 Maxillary tooth rows rather narrow in proportion to the width of 

 palate between them, in this character agreeing perfectly with those 

 of M. lucifugus. Upper molars with the full complement of second- 

 ary ridges and a well-developed protoconule. The cingulum at its 

 maximum development resembles that of M. lucifugus lucifugus, but 

 many individuals occur in which it is greatly reduced, frequently to 

 such a degree as to be nearly or quite absent from the entire lingual 

 border of the crowns. The small premolar teeth are remarkably uni- 

 form in their relations. In the upper jaw p^ and p^ are both drawn 

 inward a little from the tooth row so that the anterior small tooth is 

 overlapped by the cingulum of the canine and the posterior is over- 

 lapped to a slightly less degree by the cingulum of p^. In cross-sec- 

 tion p^ is only a little less than p^ but in profile it is much lower. The 

 cusps of both are broadly triangular and blunt in side view, that of 

 the smaller tooth {p^) reaching a level not exceeding half the height 

 of the anterior tooth. In Myotis lucifugus they are usually more 

 slender and lancet-shaped. 



Remarks. — This species is structurally much like Myotis lucifugus 

 but its size is uniformly less and the foot is, on the average, less 



