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, to 8 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 

 .ong'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. Guaymas, 

 Mexico. No. 123701. xlf. 



Genus PIZONYX Miller. 



190(i. Pizoniix Miller, Proc. Biol. Soc. Washington, XIX, p. 85, June 4 

 1906. 



Type-species. — Myotis nvesi Menegaux. 



Geographic distribution.— Known only from two localities in north- 

 western Mexico ; Cardonal 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 



