310 PALAEONTOLOGY OF ILLINOIS. 



Orodits ttjrgldus, St. J. and W. 



PI. VI, Fig. 4, 5. 



Teeth very small, robust, gently arched posteriorly. Base of mode- 

 rate depth, less than that of the crown, as also its transverse and lateral 

 diameters, moderately oblique, posterior face vertically arched in nearly 

 the same plane as the posterior coronal slope, anterior face deeply chan- 

 neled, shoulder of slight prominence, both faces coarsely punctate or 

 roughened, inferior surface broad, smooth, and gently beveled to the 

 sub-acute posterior margin, gently arched vertically, posterolateral 

 angles sharply rounded. Crown moderately and more or less regularly 

 arched between the extremities, inflated below, inbeveled along the 

 basal margius and sharply defined from the base, a strong turgid or 

 obtusely conical, more or less eccentric median prominence occupying 

 the middle region, the lateral wings regularly diminishing towards the 

 extremities, traversed by an obtuse subcentral crest, interrupted by 

 a few relatively strong tuberculations, from which descend one or two 

 prominent vertical or diverging carinas, the median cone being appa- 

 rently similarly though less strongly and more numerously plicated. 

 The coronal surfaces, when perfect, enameled and highly polished. 

 Lateral diameter of tooth about .17 inch, hight about .04. 



The form described is known by only two minute and somewhat 

 worn teeth, but which are readily recognizable by the stout build and 

 turgid median cone. It bears some likeness to 0. plicatus, N. and W., 

 with which it is most intimately allied, but apparently lacks the deli- 

 cately plicated belt characteristic of that form, besides it is relatively 

 much stouter. 



Position and locality : Pare, in the upper fish-bed of the Chester lime- 

 stone ; Chester, Illinois. 



Orodtts Alleni, St. J. and W. 



PL VH, Fig. 19. 



Teeth medium in size, laterally elongated, and strongly arched 

 upward in the midddle. Crown moderately elevated, with an obtusely 

 angular crest centrally traversing the lateral portions, the sides irregu- 

 larly corrugated vertically, the median region occupied by an obtusely 

 conical prominence, oval in outline, projecting forward and backward 

 beyond the line of the lateral wings, bordered by numerous vertical 

 folds similar to, though smaller than those in the lateral portions, and 

 • which reach upward from the base half way or more towards the sum- 

 mit of the cone ; the surface is evenly and rather finely punctate, the 



