ORDER MARSUPIALIA. 



1275 



same general type as those of the preceding genera. If this be 

 so, it would appear to countenance the view that the present group 

 should be separated from the Amphitheriidcz, but owing to the 

 damaged condition of the speci- 

 men great caution is necessary 

 in speaking positively as to the 

 nature of the teeth. 



In the second subfamily, or 

 AmphitheriifKZ^ the lower true 

 molars are differentiated into a 

 tritubercular anterior blade and 

 a posterior heel or talon. Four 



premolars are present in all those genera of which the entire lower 

 dentition is known ; and the mandibular condyle is high. The 

 upper molars are unlike the lower. Many of these genera are 

 referred by Professor Osborn to his Insectivora Primitiva. 



Before proceeding further some explanation is necessary as to 

 the structure of this type of lower molar. Following the nomen- 



Fig. 1143.— Outer aspect of the right ramus of 

 the mandible of Amphitylus Oiveni 



Stonesfield Slate. Enlarged. 



from the 

 (After Owen.) 



Fig. 1144. — Outer aspect of the left ramus of the mandible of Dryolestes vorax ; from the 

 Upper Jurassic of North America. Three times natural size, a, Canine ; c, Coronoid process ; 

 d, Angle. The incisors and first premolar are absent. (After Marsh.) 



clature adopted by Professor Flower the three cusps in the anterior 

 half of such a " tritubercular" tooth may be collectively spoken of 

 as the blade (fig. 1145, a, b, c); while the hinder part (d) may be 

 termed the talon. In the blade the cusp a is termed the anterior, 



Fig. 1 1 45.— Upper, outer, and inner views of a left lower true molar of Dasyurus. a, Anterior 

 cusp of blade (paraconid); l>, Posterior cusp of do. (protoconid); c, Inner cusp of do. (meta- 

 conid); d, Talon (hypoconid). 



the large one b the posterior, and the small one c, which is the 

 innermost, the inner cusp. According to Professor Osborn these 

 three cusps correspond to the three cusps of Priacodon (fig. 1147), 

 and in both cases he applies to them the names of para-, proto-, 



