172 



bulletin: museum of comparative zoology. 



argues from the worn condition of the triturating surface that the fare consisted 

 of hard-shelled prey, such as Brachiopods and Pelecypods, and cites an example 

 preserved in the Bergakademie in Berlin where a number of Productae are 

 contained within the abdominal cavity. It is reasonable to suppose that the 

 relative tenuity or thickness of the cutting-edge amongst different species of 

 •Janassa furnishes an approximate indication of their having subsisted on soft 

 or hard shelled prey, as the case may be. 



Janassa maxima, sp. nov. 



(Plate 3, Fig. 31 ; Plate 3, Fig. 34.) 



crown and thick cutting-margin 



Type. — Imperfect crown ; University of Nebraska. 



Teeth extremely large and robust, with very high and strongly reflexed 



Posterior two-thirds of oral surface convex 

 and covered with numerous prominent oblique plicae 

 displaying indications of wear during life. Anterior 

 face strongly convex, smooth, the posterior two-thirds 

 elevated into two abrupt longitudinal ridges which 

 are separated by a broad median longitudinal channel. 

 Anterior face showing marks of contact with next 

 oldest underlying tooth, the only indications of wear 

 during life being directly along the cutting-margin. 



Of this species only the unique tooth shown of the 

 natural size in the accompanying illustrations is known 

 at present. This is at least twice the size of the Per- 

 mian J. hituminosa (Schloth.), the largest previoush' 

 known species, which it approaches more closely than 

 any others. In fact, the relations of this new species 

 are altogether with those of Permian, rather than 

 with those of Carboniferous age. 



The whole of the root and posterior portion ot the 

 crown are missing, and a portion of the cutting-edge 

 of the crown has also been broken away. Even in 

 its mutilated condition, however, the crown exhibits a 

 total length of nearly 5 cm. Its lateral borders are 

 straight, jiroving that the tooth was not deformed by 

 interlocking with those of adjoining series. As to 

 the position in the mouth occupied by this tooth, the 

 marks of wear indicate very clearly that it belonged 

 in one of the principal series to the left of the syni- 

 physial in the upper jaw. The tooth opposed to it in 

 the lower jaw played inside its cutting-edge, and slightly to the left instead of 

 squarely against it. The asymmetrically worn condition of the cutting-edge in 



Fig. 5. 



Janassa maxima, sp 

 nov. Profile, X \- 



