AMERICAN BATS OF THE GENERA MYOTIS AND PIZONYX 99 



teeth enlarged as in M. velifer^ but small premolars showing an obvi- 

 ous tendency toward crowding and elimination. 



Ears, merribraTies, and feet. — The general features of external form 

 do not differ appreciably from those of Myotis velifer. Average 

 ratio of foot to tibia in 10 specimens, 51.9. 



Fur and color. — The fur is more full and soft than that of Myotis 

 velifer., its quality essentially as in M. hicifug'us. Tips of hairs on 

 upper surface of body distinctly burnished. 



Color above bright ochraceous tawny. Below ochraceous buff, 

 sometimes with a grayish tinge ; bases of the hairs both above and 

 below blackish-slate. Ears and membranes brownish. This phase is 

 brightest in the series of six skins from near Yuma, in the collection 

 of the Museum of Vertebrate Zoology, University of California. A 

 duller, olive phase essentially like the ordinary coloring of typical 

 Myotis iMcifugus also occurs in specimens from parts of Arizona and 

 New Mexico. Immature individuals may be nearly wood-brown 

 above, and grayish below. The ears and membranes of some indi- 

 viduals are blackish. 



Skull. — The skull is well differentiated from that of any other 

 American species of Myotis by the combination of low, flattened 

 brain case and enlarged rostrum. When the skull is viewed from 

 above (pi. 1, p. 7, fig. 8) the area of the rostrum as compared with 

 that of the brain case is greater than in any other American member 

 of the genus yet discovered. This character is obvious when the 

 skull is compared with that of Myotis velifer (pi. 1, p. 7, fig. 6) ; it 

 is very conspicuous on comparison with M. lucifugus (pi. 1, p. 7, fig. 

 12) and still more so on comparison with M. volans., one race of 

 which occurs in the same region as M. occmltus and bears a super- 

 ficial external resemblance to it. Breadth of rostrum across canines 

 decidedly greater than interorbital constriction. Distance from an- 

 terior border of alveolus of inner incisor to narrowest region of 

 interorbital constriction frequently exceeding that from narrowest 

 part of constriction to lambda. Sagittal crest always present in 

 adults but rarely as high as in average specimens of Myotis velifer. 



Teeth. — The larger cheek teeth of Myotis occultus present the same 

 feature of unusual robustness which characterizes those of M. velifer 

 and distinguishes these two species from the other American mem- 

 bers of the genus. Secondary cusps and ridges as in Myotis velifer. 

 The small premolars are peculiar in the tendency which they show 

 toward crowding and elimination. The second premolar in the 

 upper jaw {p^), rarely found to be missing in other American 

 Myotis., is more often absent than not (seventeen times in 24 speci- 

 mens) ; and if it is present, it is usually pushed out of the tooth row 

 into the angle between the first and fourth premolars, where it is not 

 visible in side view. In the lower jaw the second premolar is nor- 



