SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 435 



(No. 15,066) which retains the base of the incisor and all the inferior den- 

 tition except the vestigial antemolars. The coronoid and part of the angle 

 have been broken off. 



The median incisor is elliptical in cross-section, with the enamel con- 

 fined to the outer side. Between this tooth and the posterior premolar 

 are three closely crowded alveoles for the vestigial, single-rooted ante- 

 molars. The posterior premolar is double-rooted, compressed laterally, 

 with an anterior principal cusp and prominent heel partly overlapped by 

 the trenchant blade of the first molar. The molars are double-rooted and 

 decrease in size posteriorly. The first is greatly enlarged, as in Palceo- y 

 thentes. The ridge uniting the protoconid and paraconid is functional as 

 a sectorial blade, but is not notched as in Palceothentes. The prominent 

 metaconid is united by ridges with the protoconid and cusps of the heel. 

 These ridges form a pair of crescents, the concavity of which is directed 

 internally. The outer side of the tooth is channelled by a deep groove 

 which extends forward and inward toward the metaconid. The second 

 and third molars resemble the first in pattern. In these teeth, the proto- 

 conid-paraconid blade is considerably reduced and the tooth crown more 

 quadrangular than MT. The posterior crescent is deflected outwardly, 

 joining the anterior crescent much nearer to the protoconid than the 

 metaconid. The channel on the outer face of the tooth crown is much 

 shallower than in My. The fourth molar is a minute tooth, with button- 

 shaped crown, which, owing to its worn condition, does not show well 

 the lophodont pattern of the anterior molars. It is evident from the 

 shape of the crown that this tooth was of the same general pattern as the 

 third molar. A large mental foramen is present beneath the last vestigial 

 tooth, and a smaller foramen beneath the sectorial molar. The masseteric 

 fossa is imperforate. The angle is prominent and strongly inflected, and 

 the horizontal ramus evenly convex and of about the same depth through- 

 out beneath the molars. 



CALLOMENUS LIGATUS Ameghino. 



(Plate LXIV, figs. 5, $.) 

 Callomenus ligatus Amegh.; Enum. Syn., etc., p. 88, 1894; Bol. Acad. 



Cordoba, p. 344, 1894. 



Three species are recognized by Ameghino (1891, p. 306 ; 1894, p. "88), 

 of which but one is represented in the Princeton collection by the right 



