124 BULLETIN 51, 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 2 ) 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 1 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 deeph r 
emarginated. Lower molars, with the cusps, normal in position, and all 
well developed except the entoconid of m s , which is so reduced as to 
be practically absent. Paraconid smaller than hypoconid, especially 
in m 1? where it is also less distinct from protoconid than in m 2 and 
m 3 . Skull slender and light, the rostrum narrow and tapering, more 
than half as long as bra incase, 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 cochleae. Ears 
variable in size, usually large, j oined* across forehead. Aoseleaf 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 Micronycteris are all rather small, deli- 
cately' formed bats, having the forearm from 82 to 38 mm. in length. 
The tooth formula, short rostrum, well-developed middle lower pre- 
molar, and small audital bullye distinguish the genus from all of the 
others except the closely related Gly phony cteris and Xenoctenes.- 
Genus XENOCTENES, New. 
Type-species. — Schizostoma hirsutum Peters. 
Geographic distribution. — Costa Rica. 
Number of forms. — The type is the only species known. 
