1878.] • 67 [Cope. 



Measurements. M. 



Depth of cranium at M. 2 0138 



Length of molar series along base 0080 



Diameter of second molar { anteroposterior 0016 



\ transverse 0020 



Width of face of superior incisor 0020 



Meniscomys hippodus, gen. et sp. nov. 



Gen. OJiar. The characters of this genus are derived from the dentition 

 of both jaws, and from portions of the cranium which are preserved. The 

 molars are rooted, and number f. Those of the superior series are with- 

 out enamel inflections, and the triturating surface exhibits two external 

 and one internal crescentic sections of the investing enamel. On the sec- 

 ond superior molar there are three external crescents in the typical species ; 

 and the first molar is simply conic. Between the inner and external cres- 

 cents, there are the curved edges of enamel plates directed obliquely and 

 transversely. The grinding surfaces of the inferior molars display in the 

 unworn condition, two L-shaped transverse crests, connected longitu- 

 dinally on the median line ; on wearing, the lateral emarginations of the 

 enamel become shallower, disappearing from the inner side, but remaining 

 on the outer. Incisor teeth not grooved. Foramen infraorbitale anterius, 

 if present, elevated in position and near orbit. 



The characters of the dentition of this genus resemble those of the genus 

 Pteromys, which is now confined to Asia and the Malaysian Archipelago. 

 The superior molars differ from those of Pteromys in wanting all reentrant 

 enamel inflection. Specimens in my collection indicate two species of 

 Meniscomys. 



Specif. Char. Superior molars with a vertical ridge from the points of 

 junction of the crescents on the external side ; there are thus two on the 

 second molar, and one eacli on the third and fourth. Within each of the 

 external crescents is another crescentic edge of a pair of vertical enamel 

 plates, and the inner marginal crescent sends off a short transverse branch 

 towards them. With attrition, all these crests unite by their extremities, 

 enclosing four distinct lakes, which, after still further wear, disappear. 

 Attrition pi-oduces a similar result in the inferior molars, viz. : two pairs of 

 crescents enclosing four lakes, which ultimately wear out. The inferior 

 incisor has a shallow concavity on its anterior face. 



The maxillary bone, anterior to the molar teeth, is shorter than the pre- 

 maxillary. The incisive foramina are entirely in the latter. The sides 

 and superior aspect of the muzzle are regularly convex in transverse sec- 

 tion. The inferior incisive alveolus is enclosed entirely in the plane of the 

 ramus, and extends posteriorly to below the last molar tooth. The masse- 

 teric ridge is very oblique, and rises to a median point below the second 

 molar. The coronoid process rises from the front of the last molar. 



Measurements. M. 



Length of superior molar series 008 



