AMERICAN BATS OF THE GENERA MYOTIS AND PIZONYX 207 



width across bases of canines is obviously less than the interorbital 

 constriction; in M. simus the width across canines equals or exceeds 

 the interorbital constriction (among 12 skulls it equals the constric- 

 tion in 3 and exceeds it in 9). The mandible is conspicuously deeper 

 than that of Myotis albescens and the angular process is more robust. 



Teeth. — The teeth are in general more robust than those of Myotis 

 albescens., in this respect about equaling those of M. chilo'en^is. The 

 canines, in particular, are larger than those of other South American 

 species. In both the maxilla and mandible there is a tendency to 

 crowding of the small premolars and reduction in the size of the 

 second small tooth. This process is carried so far in the upper jaw 

 that the second small tooth is usually hidden by the cingulum of the 

 large premolar when the tooth row is viewed from the outer side. 

 Though crowded, the second tooth is present in all of the specimens 

 examined. Upper molars well characterized by the narrowness of 

 the internal segment resulting from the small size and slight distinct- 

 ness of the hypocone from the base of the somewhat unusually high 

 protocone. Secondary cusps and ridges not well developed, the pro- 

 toconule frequently absent or indistinct. 



Measureinents. — For measurements see tables, page 208. 



SfeGvmens examined. — Sixteen, from the following localities: 



ECUADOR: Mouth of the Curaray River, 13 skins (A. M. N. H.). 

 BRAZIL: Rio Yurua, Amazonas, 3 skins without skulls (B. M.). 



Remarks. — Myotis simus is so different from all other known 

 American species of Myotis that it can not be confused with any of 

 them. Its shorty woolly fur, small ears, and entirely naked membranes 

 give it a superficial appearance which recalls some other genus : Pipis- 

 trellus or ScotophiJivs., Thomas suggested in the original description. 

 Among the American members of the genus there is only one, the 

 otherwise very different Myotis grisescens of southeastern United 

 States, which shares with M. simMs the peculiarity of having the wing 

 membrane inserted at the ankle. Obviously, however, there is no 

 specially close relationship between these two species, the cranial 

 and dental characters of which differ widely from each other. The 

 unusual breadth of the rostrum anteriorly differentiates Myotis simus 

 among the South American members of the genus ; in North America 

 the same character is found in the otherwise very different Myotis 

 velifer and M. occultus. 



The peculiar quality of the fur in Myotis simus is a character 

 which is unique among the known American members of the genus. 

 The same may be said of the heavy mandible and unusually high 

 sagittal crest, two characters which are probably correlated with 

 each other and with the shortening of the tooth row as elements of 

 a general strengthening of the chewing machine. 



