THE FAMILIES AND GENERA OF BATS. 
39 
This aberrant type (Plates V and YI) is found throughout the large 
subfamily Stenoderminse. In the maxillary teeth the paracone and 
metacone, with occasionally an intermediate cusp, perhaps the rem- 
nant of the mesostyle, form a cutting edge at outer margin, usually 
with a distinct cingulum in the normal position and an equally well- 
developed ridge on inner side extending from point or base of 
paracone to posterior base of metacone; the crowns are increased in 
width to form a large crushing area, the surface of which is usually 
roughened by folds or wrinkles, from which may be developed a 
definite protoconule and metaconule (Plate VI, fig. 3) ; and a very 
large hypocone is often as a conspicuous postero-internal heel, which, 
in the most extreme instances, occupies the entire lingual side of the 
tooth and assumes the appearance of a protocone, causing the latter to 
occupy the relative position of a protoconule, though always recog- 
nizable by its large size (Plate VI, fig. 2). In the mandibular teeth 
a similar widening and flattening of the crowns has taken place ; the 
surface of the enamel is of the same character; the paraconid is 
absent, and the metaconid and entoconid tend to assume a subulate 
form, rising abruptly from the flattened surface of the crown (Plate 
V, fig. 2). 
The Stenodermine dentition most nearly resembles the Sturnirine 
type, and it seems probable that the two had a common origin, though 
the Stenodermine type has now become much the more aberrant. 
Among the different genera there is considerable variation in the 
details of the tooth structure, though never enough to obscure the 
pecidiar appearance characteristic of the type. The nearest approach 
to the Sturnirinae is seen in V ampyrops and Chiroderma , both of 
which lack all definite trace of the hypocone.® 
In the former the surface of the crowns is nearly smooth and the 
inner cingulum of the outer cusps is well developed, while in the 
latter the croAvn surface is coarsely wrinkled and the inner cingulum 
is absent. Either genus is readily distinguishable from Sturnira by 
the increased breadth of the crowns and the consequent replacing of 
the longitudinal groove by a wide crushing area. In TJroderma 
(Plate VI, fig. 1), the second upper molar shows a small shelf-like 
postero-internal projection, while in the first molar this has increased 
in size and assumed a distinct cusp-like form. About the same stage 
is represented by the first molar of Pygoderma , while an evident trace 
of the small hypocone can usually be detected in the greatly reduced 
second molar. A very rudimentary metaconule is present in m 1 and 
m 2 of TJroderma , and a similar but larger cusp is represented in the 
o The faintest possible suggestion of this cusp, or rather of a cingulum in the 
position that the cusp occupies in other genera, is present in some specimens of 
V ampyrops lineatus. 
