THE FAMILIES AND GENERA OF BATS. 39 



This aberrant type (Plates V and VI) 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 cin'gulum 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 

 peculiar appearance characteristic of the type. The nearest approach 

 to the Sturnirinae is seen in Vampyrops and Chiroderma, both of 

 which lack all definite trace of the hypocone. 11 



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 crown 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 Uroderma 

 (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 z of Uroderma, and a similar but larger cusp is represented in the 



a 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 

 Vampyrops lineatus. 



