176 BULLETIN 144, UNITED STATES NATIONAL MUSEUM 



within the membrane, though occasionally a minute tip is free. The 

 fur of the body extends out on the uropatagium, both above and 

 below, to or a little beyond a line joining the knees. 



Foot. — The foot is small and delicate in proportion with the gen- 

 eral small size of the animal. In series of specimens from different 

 localities the average ratio of foot to tibia ranges from about 43 to 

 about 53. Calcar a little shorter than the free border of the inter- 

 femoral membrane (about 14: 19 mm.), often though not constantly 

 provided with a small keel, and usually ending in a minute projecting 

 lobule. 



Fur and color. — The pelage is soft but not especially full and silky 

 in quality ; the hairs on the back about 5 mm. in length. The color 

 of the hairs is everywhere blackish plumbeous at base; tips brown 

 with a faint gloss and usually so dark as to present no conspicuous 

 contrast with the under color; entire ventral surface less darkened 

 and more tinged with yellowish than back. There is a slight tend- 

 ency to dichromatism shown by the rare occurrence of individuals 

 with orange-suffused pelage. 



Skull. — The skull is small and delicately formed. Profile of the 

 forehead rising rather abruptly; brain case distinctly globular. The 

 temporal ridges often form a distinct though low sagittal crest. The 

 rostrum is relatively broad in proportion to its length, with the width 

 across the molars slightly exceeding the length of the maxillary 

 tooth row (front of canine to back of last molar). 



Teeth. — The two minute upper premolars stand usually full in 

 the tooth row, though rarely the second may be crowded inward from 

 the line. The cingulum is distinct and the cusp of the posterior tooth 

 reaches about half way to the tip of the anterior. The upper molars 

 resemble those of the North American Myotis lucifugus in the full 

 development of the secondary cusps and ridges and in the breadth 

 and distinctness of the cingulum. The transverse diameter of the 

 crown in m^ and w^ is less proportionately to the antero-posterior 

 diameter than in M. lucifugus. 



Remarks. — Myotis nigricans is a bat peculiar to the warmer parts 

 of America. Its range probably meets that of Myotis calif ornicus in 

 southern Mexico. Though allied to M. californicus and structurally 

 not very different from it, Myotis nigricans is undoubtedly a distinct 

 species characterized by the almost uniform coloration of the hairs 

 from base to tip, the shorter third metacarpal (which does not reach 

 the elbow as it usually does in M. californicus)., more robust foot 

 and shorter tail and ears. The skull has a slightly more elevated 

 occiput, and the width across the molars is increased so that this dis- 

 tance tends to be perceptibly greater than the maxillary tooth row 

 instead of about equal to it. 



