124 BULLETIN 57, UNITED STATES NATIONAL MUSEUM. 



side into two very unequal lobes ; anterior face convex, posterior con- 

 cave; cingulum distinct. Outer incisor scarcely extending beyond 

 cingulum of inner, its crown flat, with slight cusp on inner side and 

 roundish in outline. Lower incisors small, simple, forming a continu- 

 ous, slightly convex row between canines, the crowns subquadrate in 

 outline, when viewed from above, the cutting edges faintly bifid and 

 the anterior face of each tooth distinctly concave. Inner tooth of 

 each pair slightly larger than outer. Canines strong, simple, with 

 well-developed cingula, but no supplemental cusps, the anterior face 

 of the shaft smoothly rounded. Anterior upper premolar (pm 3 ) 

 large, its area when viewed from the side about equal to that of pos- 

 terior tooth (pm 4 ) , crown strongly trenchant. Posterior upper pre- 

 molar (pm 4 ), with main cusp straight, situated at or near middle of 

 crown ; style well developed, but inner cusp obsolete, and longitudi- 

 nal groove scarcely indicated. First lower premolar (pm „) of much 

 the same form, though smaller. Second lower premolar nearly as 

 large or slightly smaller than first or third, perfectly in the toothrow. 

 Other teeth showing no special peculiarities. Molars normal, though 

 the paracone and metacone of m x and m 2 are situated farther out- 

 ward than usual, causing a slight flatness in the W pattern; hypocone 

 low but distinct. Third upper molar with less than half the crown 

 area of m 2 , its four cusps distinct, but the two commissures deeply 

 emarginated. Lower molars, with the cusps, normal in position, and all 

 well developed except the entoconid of m .,, which is so reduced as to 

 be practically absent. Paraconid smaller than hypoconid, especially 

 in m u where it is also less distinct from protoconid than -in m , and 

 m 3 . Skull slender and light, the rostrum narrow and tapering, more 

 than half as long as braincase, its upper surface evenly convex later- 

 ally. Braincase rather large, its surface with no conspicuous ridges. 

 Anteriorly the forehead rises rather abruptly, and posteriorly the 

 metencephalon is marked off by a distinct constriction. Audital 

 bullae small and well developed, covering about half of cochlea;. Ears 

 variable in size, usually large, joined across forehead. Xoseleaf well 

 developed. Tail short but distinct, extending about to middle of very 

 wide interfemoral membrane. 



Species examined. — I have examined all of the known forms. 



Remarks. — The species of Micronyeteris are all rather small, deli- 

 cately formed bats, having the forearm from 32 to 38 mm. in length. 

 The tooth formula, short rostrum, well-developed middle lower pre- 

 molar, and small audital bulla? distinguish the genus from all of the 

 others except the closely related GlyphonyHerls and Xenoctenes. 



Genus XENOCTENES, New. 

 Type-species. — Srhizoxtoma, hirsnttim Peters. 

 Geographic distribution,. — Costa Rica. 

 Number of forms.— -The type is the only species known. 



