202 BULLETIN 51, UNITED STATES NATIONAL MUSEUM. 
cutting edge, the third much wider, subterete, with three or four 
tubercles. Canines well developed, simple, with distinct though rather 
small cingulum and no secondary cusps. Cheek teeth both above and 
below strictly normal, m 1 and m 2 rather narrow on inner edge and 
with hypocone absent or very imperfectly developed, m 3 with three 
commissures and four or five cusps, according to the varying condi- 
tion of the metacone, m 3 , with second triangle smaller than first, but 
with all the elements of the tooth complete. Skull slender and lightly 
built, without special peculiarities of form, the rostrum nearly as 
.on g as braincase, the depth of braincase, including audital bulla, 
about equal to mastoid breadth, the sagittal crest low, but usually 
distinct, the palate deeply emarginate in front, abruptly contracted 
behind, the sides of its posterior exten- 
sion parallel. Audital bullae well devel- 
oped and covering more than half sur- 
face of cochleae, but simple in form and 
not very large, their diameter about equal 
to the distance between them. Ear well 
developed, slender, occasionally rather 
large ; tragus slender and nearly or 
quite straight. Foot very variable in 
size, but never peculiar in form. Tail 
about as long as outstretched leg. Inter- 
femoral membrane large, its surface 
furred at extreme base above. 
Species examined. — I have examined 
about half the known forms of Myotis. 
Remarks. — Myotis appears to be the 
most primitve genus of Vespertilionidse, 
as it not only retains the maximum number of teeth known in the 
order, but it also has the slightest possible degree of special modifica- 
tion in external form. 
Fig. 31.— Pizonyx vivesi. 
Mexico. No. 123701. 
Genus PIZONYX Miller. 
1906. Pizonyx Miller, Proc. Biol. Soc. Washington, XIX, p. 85, June 4, 
1906. 
Type- species— Myotis vivesi Menegaux. 
Geographic distribution. — Known only from two localities in north- 
western Mexico ; Cardona! Island, Gulf of California, and Guaymas, 
Sonora. 
Number of forms . — Only the type species is thus far known. 
Characters— Like Myotis , but with foot (claws included) as long as 
tibia, the toes and claws greatly compressed, so that width of claw 
is only about one-eighth the height at base ; wing with large glandular 
