410 EXTINCT MAMMALIA OF NORTH AMERICA. 



reaching across the median valley and also anteriorly, but ceasing and becoming 

 obsolete behind. 



Two cusps or lobes project at the outer part of the crown of the true molars, and 

 three smaller ones internally. Of the outer cusps the anterior is the higher and 

 narrower. Of the inner ones the posterior two are nearly equal, and the anterior is 

 the smallest ; most so in the second molar. They are all three-sided pyramids, each 

 with one face directed inwardly and two outwardly. Their height is not greater than 

 their width, nor are they very sharply pointed. The borders defining the inner sur- 

 face of the antero-external cusps conjoin the antero-interniil two cusps, including a 

 small depression. Of the borders defining the inner concave surface of the postero- 

 external cusp, the front one joins the posterior surface of the antero-external cusp, 

 while the back one joins the postero-internal cusp. 



The space occupied by the m.olar series was about six and a half lines. The length 

 of the crown of the third premolar is one and one-fifth lines ; the breadth one line. 

 Length of crown of second premolar five-sixths of a line ; breadth one and one-fifth 

 lines. Breadth of first true molar one and one-fourth lines. 



DROMATHERIUM. 



Dromatlieriiixii silvestre. 



Emmons: Am. Geol. 1857, 93, Fig. 66 ; Manual Geol. 1860, 171, Fig. 152. Leidy : Proc. Ac. 

 Nat. Sc. 1857, 150 ; 1859, 162. Owen : Palffiontology, 1860, 302. Dana : Manual of Geology 

 1863, 429, Fig. 650. 

 Insectivorous mammal, Emmons: Pr. Am. As. Adv. Sc. 1858, 78. 



Indicated by two halves of lower jaws, of different individuals, discovered by Prof. 

 E. Emmons in the coal of Chatham Co., N. C. One of the specimens is preserved in 

 the Museum of the Academy. The oldest known mammal yet found in America. 

 Triassic. 



MARSUPIALIA. 



DIDELPHYS. 



Didelphys virginiana. 



Holmes : i'ost-pliuc. Fos. S. Carol. 1860, II, 116, PI. XXIII, Fig. 2. 



Quaternary ? and recent. 



