VEETEBEATES. 75 



can scarcely be questioned. Its salient contrasts, compared with 

 the forms associated under the latter specific designation, consist in 

 the more symmetrical outline, and coarser, irregular character of 

 the coronal punctse. 



Geological position and locality: Chester limestone ; Chester, Illinois. 



GENUS T^NIODUS, L. de Koninck Mss. 



Teeth representing the posterior form of the upper jaw attain large 

 size, sub-rhomboidal or oblique-trapezoidal in outline, moderately 

 arched from within outward, and inrolled, more or less obliquely, 

 outward and forward. Lateral borders regularly and gradually con- 

 verging toward the outer extremity, which may be truncate, as in 

 Psephodus, of moderate depth, inferior or basal portion channeled 

 and distinctly denned from the coronal fold, which forms a sort of 

 coping along the upper edge ; antero-lateral border relatively short, 

 having a more or less oblique outward and forward course and slightly 

 concave curvature between the obtuse inner angle and point of inroll- 

 ment ; postero-lateral border gently and regularly arched from the sub- 

 acute posterior angle, and gradually converging outward with slightly 

 greater obliquity than the opposite border; inner margin making a 

 gentle ^curvature from the posterior angle forward to the rounded 

 angle at the base of the coronal prominence, where it is suddenly 

 deflected forward with a slight concavity to the anterior angle, 

 making a very obtuse angle with the posterior half of its course. 

 Coronal contour presenting a simple posterior prominence culmin- 

 ating in a low, rounded crest, the broad posterior slope usually 

 slightly convex, though sometimes faintly depressed, that on the 

 opposite side apparently more abrupt and merging into the slightly 

 depressed anterior area ; the surface is more or less distinctly un- 

 dulated by transverse ridges separated by narrow furrows, conform- 

 ing in outline to the inner margin. The usual punctate structure 

 occurs over the entire coronal region, the pores showing a tendency 

 to irregular elongation in the axis of the transverse sulci. Inferior 

 surface of teeth showing the dense inferior layer longitudinally 

 striated; thickest beneath the coronal ridge. 



The foregoing diagnosis applies to a group of teeth meagerly rep- 

 resented in the collections by the form homologous with the posterior 

 teeth of the upper jaws of Cochliodus and allied genera. A single, 

 nearly perfect specimen from the Carboniferous limestone of Vesi, 



