212 BULLETIN 144, UNITED STATES NATIONAL MUSEUM 



back, the hairs mostly without darker bases except those near wing 

 membranes. 



Skull. — The skull (pi. 1, p. 7, fig. 1) is immediately distinguishable 

 from that of any American Myotis by its much greater size (total 

 length about 22, while no American Myotis is yet known in which 

 the skull ever attains a total length of 18 mm.). When compared 

 with the skull of Myotis velifer, the species which most nearly ap- 

 proaches it in size (maximum total length IT.6), that of Pizonyx 

 vivesi is seen to present some obvious peculiarities of form. The 

 brain case is less elevated behind and less abruptly constricted ante- 

 riorly ; its sagittal crest is low and inconspicuous. The longitudinal 

 median groove on the rostrum is relatively deeper and better defined. 

 When the skull is placed on a flat surface the alveolar line rises at a 

 noticeably greater angle than in Myotis velifer^ so that the tips of the 

 high canines are elevated conspicuously above the surface on which 

 the skull is resting instead of being brought almost in contact with it 

 as is the case with the low canines of the smaller animal. 



Teeth. — Apart from their greater size the teeth differ from those 

 of the American species of Myotis in a general tendency toward 

 heightening and slenderness of the cusps, a tendency which is espe- 

 cially noticeable in the canines and premolars. The height of the 

 upper canine above alveolus is equal to decidedly more than the com- 

 bined crown length of the four large cheek teeth, while in Myotis 

 velifer it is as decidedly less than half this length. Both of the small 

 premolars, mandibular as well as maxillary, are obviously heightened, 

 and the second tooth in each pair exceeds the first both in height as 

 seen from the side and in crown area as seen in apical view, a condi- 

 tion unknown in any American Myotis. In the mandible this height- 

 ening of the second premolar is so great that the profile of the entire 

 row of cusp summits does not show the abrupt fall in front of the 

 large premolar which is so characteristic of the cusp profile in ordi- 

 nary Myotis. The incisors present no marked peculiarities. Molars 

 normal in form; m^ not reduced. All of the cusps share in the 

 general tendency to heightening characteristic of the entire dentition, 

 but this tendency is here less pronounced than it is in the canines and 

 premolars. In m} and in? the small ridge which, in Myotis, extends 

 from the base of the paracone to the protoconule usually runs to the 

 protocone, leaving the very rudimentary protoconule, when present 

 at all (usually absent), isolated on the margin of the crown. (Fig. 

 Id, p. 8.) 



Measurements. — The measurements of the cotypes (both females) 

 as noted by Miller in 1904 are as follows : Total length, 145 and 140 ; 

 tail, 70 and 69; tibia, 24 and 24.6; foot, 23 and 23.8; longest claw, 

 10 and 10; forearm, 62 and 60; thumb, 12.2 and 12.6; claw of thumb. 

 2.4 and 3 ; second finger, 62 and 60 ; third finger, 120 and 120 ; fourth 



