EASTMAN : CARBOxVIFEIJOUS FISHES FROM THE CENTRAL WEST. 173 



/. bituminosa is very distinctly shown in Hancock and Howse's figures,^ and 

 also in Jaekel's.^ There can be little doubt that the action of the jaws upon 

 one another was similar to that obtaining in modern Gyninodonts and Chi- 

 niaeras. It has been stated in the definition of this species that the anterixjr 

 face of the crown exhiljits marks of contact with the next older tooth which 

 it displaced. These markings are of two kinds. In the first place a raised 

 line extending parallel with the cutting-edge at a distance of about a centi- 

 meter behind it (PI. 3, Fig. 24) demarcates the area overlapped by the pre- 

 ceding tooth; in other words, it divides the exposed cutting-edge from the 

 covared portion. Secondly, the longitudinal ridges on the anterior face dis- 

 play a number of parallel facettes caused by the impress of the oblique folds 

 on tlie triturating surface of the next older tooth which this one displaced. 

 Similar markings have been observed on the anterior face of teeth belonging to 

 /. bituminosa, and this interpretation is given of them by Messrs. Hancock and 

 Howse.3 The thickness of the cutting-margin ((/. Text-fig. 5) and generally 

 stout condition of the present specimen render it probable that the creature 

 subsisted on hard-shelled prey. 



Formation aiid Locality. — Atchison shales (Missourian) ; Richfield, Nebraska. 



Janassa unguicula, sp. nov. 



(Plate 2, Fig. 13.) 



Type. — Imperfect tooth ; University of Nebraska. 



Teeth delicate and of moderate size ; crown much reflexed, regularly arched 

 from side to side, and with a knife-edge trenchant margin. Outer coronal face 

 smooth, posterior face entirely covered with fine longitudinal striae. Form of 

 tiiturating surface and root unknown. 



) 



Fig. 6. 



Janassa unguicula, sp. nov. Outer face of crown, X {■ A, Vertical section. B, 

 Oral aspect, viewed from above, X \. 



This species is represented by a unique specimen from the Missourian of 

 Cedar Creek, Nebraska, shown of the natural size in Plate 2, Fig. 13, and Text- 

 fig. 6. Only the cutting portion of the crown is preserved, the crushing sur- 

 face (if one was indeed present) and root having been broken away. The size 



1 Ann. Mag. Nat. Hist. (4), Vol. V., 1870, PI. II., Fig. 2. 



■^ Zeitschr. deutsch. geol. Ges., Vol. LI., 1899, PI. XIV., Fig. 2. 



^ Loc. cit., p. 55. 



