370 PALEONTOLOGY OF ILLINOIS. 



upward, sometimes curved downward or irregularly sin uose, and limited 

 by a narrow, though well marked coronal belt consisting of as many as 

 five imbrications; coronal surfaces smooth or faintly striated, striato- 

 punctate along the worn crest. Basal area broad, gently depressed and 

 more or less distinctly defined from the root, which latter varies consid- 

 erably iu depth in different individuals, autero-posteriorly compressed or 

 wedge-shaped, sharply defined from the projecting margin of the con- 

 cave crown-face, descending more or less obliquely backward or out- 

 ward, laterally converging, inferior surface slightly oblique to the 

 horizontal plane of the crown, but generally obscurely defined and 

 often terminated in a sharp edge ; both faces more or less coarsely 

 roughened. A small symmetrical and unusually well preserved tooth 

 measures in lateral diameter .32 inch, hight of concave crown face .15, 

 hight of convex face .07, greatest diameter of root .23, depth of inner 

 face about .05 inch. 



This form presents considerable individual variability, which proba- 

 bly, in consequence of the larger number of specimens which exist in the 

 collections, is even more striking than in the case of T. beUicinctus, with 

 which it is intimately allied. Eegarding the specific identity of these 

 varied forms, the only evidence is their association in the same stratum 

 and certain well-defined peculiarities of coronal or basal conformation 

 common to all, however variable and dissimilar in outline are the 

 extreme examples. Compared with T. beUicinctus, besides its smaller 

 size, it is distinguishable by the more strongly developed coronal bands 

 encircling the basal margins of the crown, and the relatively deeper 

 and more oblique root; all the specimens thus far known are less elon- 

 gated laterally, and of less symmetrical proportions, upon which latter 

 feature, however, little stress should be placed in the present state of 

 our knowledge of the Chester forms. 



The particular horizons and localities which have afforded indubita- 

 ble examples of the present form, also afford teeth having the same 

 general outline, but which present unmistakable evidence of extreme 

 abrasion in the roughened coronal portion and the sulcation of the 

 basal area immediately beneath the convex coronal border. In these 

 teeth the convex crown-face is worn down to an obtuse ridge, the 

 coronal folds being obsolete in either face, though along the inner 

 margin a strong ridge defines the basal limits, while the intermediate 

 space presents a more or less deep, broad excavation, which occupies 

 the concave crown-face; in all these teeth the root is wedge-shaped 

 and terminated inferiorly in a sharp edge. Notwithstanding the 

 absence of specimens showing a gradation into the more perfect teeth 

 of the above description, as in the instance of T. lellicinctus, their rela- 

 tionship seems to be unmistakable, since they exhibit the same eviden- 



