40 BULLETIN 5 1 , UNITED STATES NATIONAL MUSEUM. 
same teeth of Stenoderma as figured by Peters.® Artibeus (Plate V, 
fig. 1 ) , shows the hypocone of m 1 large and in characteristic position 
for the group — that is, mostly lingual to the protocone. In m 2 , how- 
ever, the condition is about the same as in Uroderma. The genera 
Ariteus , Phyllops , Ardops , and Sphceronycteris have the hypocone 
of m 2 well developed and of the same form as that in m 1 , though not 
as large. This is accompanied by an increased widening of the 
crowns. The maximum of widening is seen in the first molar of 
Centurio (Plate VI, fig. 2), where the distance from hypocone to 
protocone is nearly equal to that from protocone to paracone, and the 
points of these three cusps are exactly in line with each other. 
Between the bases of the paracone and metacone in the first and 
second molar of TJroderma (Plate VI, fig. 1) may be detected a slight 
depression, the middle of which is occupied by a faintly marked 
groove. This is probably the first trace of the peculiar structure that 
forms so conspicuous a feature in the second molar of each jaw in 
E ctophylla. 
As already pointed out, a minute metaconule is present in Uroderma 
and Stenoderma , apparently developed as a specialization of the 
rugosity of the crushing surface. The same cusp is present in the first 
and second molars of Brachyphylla (Plate VI, fig. 3) as a low though 
evident longitudinal or oblique ridge, best developed in m 2 . In the 
first molar there is a protoconule of somewhat the same size and form, 
though smaller and more strictly longitudinal. This cusp becomes 
of considerable importance in the second molar, where its height and 
its basal area are both fully half as great as in the protocone, which 
the new cusp resembles in form. So strong is this resemblance that 
were it not for its position on the crown and for the reversal of the 
relative sizes the protoconule might be mistaken for the protocone 
and the protocone for the hypocone of a somewhat aberrant tooth 
of the usual Stenodermine type. In the third molar a similar cusp 
is present, though not as high or as well defined. The inner margin 
of the teeth is without trace of cingulum or shelf-like rudiment of 
the hypocone. In the mandicular teeth the intermediate cusps are 
rather well developed in m 2 , though absent or barely indicated in m x 
and in m 3 . When present they assume the form of low, subterete 
elevations at base of metaconid and entoconid. The very peculiar 
arrangement of cusps in this otherwise primitive genus is probably 
a development from a type in which the teeth resembled those of 
Chiroderma. 
The Pteropine dentition (Plates VII, VIII) though at first sight 
strikingly different from that of the typical Microchiroptera, has 
undoubtedly been developed from a primitive type similar to that 
a Monatsber. k. preuss. Akad. Wissensch., Berlin, 1876, plate facing p. 434. 
