VERTEBRATES. 89 



tion channeled, positively extended beyond the limits of the narrow 

 inbeveled fold of the coronal enamel ; the antero-lateral border simi- 

 larly denned. Posterior lobe of the crown gently arched transversely, 

 in front merging into the plane anterior surface from which it is 

 apparently obscurely denned. Surface, along the inner margin pre- 

 serving the dense enamel layer, with distinct lines of growth parallel 

 with that margin ; the worn triturating surface showing a minute 

 punctate structure, the pores of extreme minuteness and relatively 

 widely spaced. Greatest breadth across inner margin 9.5 m m, the 

 basal spur extending a millimeter farther ; length along antero-lateral 

 border about 4.5 m m. 



Only a solitary example of the present species is known to us. 

 The coronal contour, although much worn by use, presents charac. 

 teristics consonant with Vaticinodus, specifically differing from its 

 Coal Measure congener V. carbonarius, by the relative great diame- 

 ter in the direction of inrollment, the broad and uniformly arched 

 inner margin, also the more obscure definition of the coronal promi- 

 nence. The arched condition of the postero-lateral border, and the 

 entirely dissimilar coronal contour distinguishes the tooth from the 

 homologous form of Orthopleurodus, with which it is associated in 

 the same deposits. 



Geological position and locality: Upper Coal Measures ; upper lime- 

 stone at LaSalle, 111. 



GENUS DELTOPTYCHIUS, Agassiz. 



Deltoptychius, Agassiz, MSS., 1859, etc., D. (Cochliodus) acutus, Ag. 



Teeth possessing the general characteristics attributable to the 

 family Cochliodontidae. 



Posterior teeth of the lower jaw trigonal in outline, generally 

 strongly built", and moderately arched in the direction of inrollment. 

 Antero-lateral border partaking of a slight sigmoidal curvature in 

 consonance with the spiral inrollment of the tooth, defined by a 

 nearly vertical wall forming at the brink a right angle with the 

 superior crown surface, and enveloped to a greater or less extent in 

 the coronal enamel which usually constitutes a slight inbeveled fold 

 well defined from the basal portion; postero-lateral border more or 

 less oblique to the opposite border, toward which it converges at the 

 outer extremity, defined above by a shallow enamel fold, beneath 

 which the basal rim projects downward and outward, terminating 

 posteriorly in a more or less produced spur; inner margin broadly 



