NEW FOSSIL MAMMAL. 527 



(protoconid) of its trigonid is much more worn than the two 

 inner cusps, of which the anterior (paraconid) is the larger and 

 well separated from the posterior (metaconid) by a deep cleft. 

 Its posterior heel (talonid) is bordered by a much raised rim, 

 whicJi is sharply separated by a groove from the trigonid, and 

 bears one large outer cusp (hypoconid), a smaller inner cusp 

 (entoconid), and a still smaller posterior cusp (hypoconulid), all 

 considerably worn. In the second molar (ni. 2) the three cusps 

 of the trigonid are about equally worn, and the raised rim of the 

 talonid closely resembles that of the third molar already described, 

 but appears to be more worn. The first molar, represented only 

 by fragments of the roots, is comparatively small, ^'he fourth 

 premolar {pin. 4) is very large and inserted by two divei'gent 

 I'oots, of which the posterior is the stouter, and both are marked 

 by slight vertical flutings. Its crown consists of a tumid antero- 

 posteriorly elongated cone, with a small, well separated pillar-like 

 cusp behind. The apices of the cone and cusp are truncated by 

 wear, and the large worn surface of the crown is extended by a 

 second small surface of wear antero-internally. The enamel of 

 its outer face exhibits faint traces of vertical wrinkling. The 

 small third premolar is represented only by its two roots {pm. 3), 

 and the diminvitive foremost premolar, generally regarded in 

 opossums as the first of the normal series, is shown by its simple 

 root (^«i. 1) to have been displaced inwards. The socket for the 

 procumbent canine (c.) is relatively large ; and the shape of the 

 broken end of the symphysis suggests that the incisors were veiy 

 small. 



The following are some of the principal measurements, in 

 millimetres : — 



Total length of dental series behind canine ... 30' 



M. 4, maximum length (about) 6 



M. 3, „ length 5-5 



,, breadth 3"5 



M. 2, „ length 4-5 



,, breadth 3*5 



M. 1, „ length (about) 4 



Pm. 4, „ length 5-5 



,, breadth 3'5 



Pm. 3, „ length (about) 4*5 



The dentition thus described is closely similar to that of the 

 existing Dldelphys, but differs in the shape of the large hinder 

 premolar, and doubtless represents a distinct genus. Molar teeth 

 of the same pattern from the Cretaceous Laramie Formation 

 of Wyoming, U.S.A., were named Cimolestes by Marsh*, who 

 assigned them to an imperfect jaw in which the sockets indicated 



* O. C. Marsh, " Discovery of Cretaceous Mammalia," Amer. Journ. Sci [31 

 vol. xxxviii. (1889) p. 89. " 



