162 PAL^EONOTOLOGY OF ILLINOIS. 



opposed articular border of the terminal tooth, basal border deep, 

 inbeveled, double-furrowed, terminating inferiorly in a narrow rim, 

 and bordered above by the relatively strong, rounded, inbeveled, 

 enamel fold; antero-lateral border relatively very short. The 

 enamel fold inbeveled to the channeled basal border and constitut- 

 ing more than half the height of the border; inner margin mak- 

 ing a slight sigmoidal curvature from the acutely rounded posterior 

 angle to the obtuse anterior angle, inferiorly inbeveled in worn ex- 

 amples. Coronal surface nearly plane transversely, culminating in 

 a low, obscurely denned ridge close upon and parallel with the 

 postero-lateral border, the broad anterior slope merging into the 

 very shallow depressed belt traversing the anterior portion of the 

 coronal area; surface marked by distinct transverse undulations 

 and furrows parallel with the inner margin, inner edge enveloped 

 in a dense enamel coating, immediately forward of which the worn 

 surface exhibits irregular verrucose markings, and over the much 

 worn outer half the usual punctate structure appears, the punctae 

 displaying marked tendency to irregular elongation in various direc- 

 tions, in all which particulars the teeth bear most intimate resem- 

 blance to the associated forms of the species. A mature tooth 

 measures across the inner margin 7.3 m m ; along the postero-lateral 

 border to point of inrollment about 10.5 m m ; antero-lateral border 

 about 4mm. 



Maxillary posterior teeth narrow triangular or subcuneate in out- 

 line, gently arched longitudinally. The anterior portion of the inner 

 margin diverges at a very slight angle with the antero-lateral bor- 

 der, or making nearly a right angle with the portion behind the 

 abruptly rounded base of the coronal ridge, slightly concave in 

 passing the posterior depression into the slightly produced posterior 

 angle; postero-lateral border very gradually converging toward the 

 outer extremity, which is suddenly inrolled; both the antero 

 and the postero-lateral borders are marked by the narrow enamel 

 fold, inbeveled to the channeled basal border, which latter in the 

 anterior border is exceedingly shallow compared with it: greater 

 inbeveled depth in the posterior border. Coronal prominence rising 

 abruptly from the antero-lateral border, regularly arched transversely, 

 more gently descending into the posterior depression, which is 

 traversed by a faint angulation defining the inner limits of the 

 narrow and somewhat sharply upraised posterior wing. Surface 

 markings agreeing with what has already been observed in relation 

 to the opposed mandibular teeth, even to the details of the irregular 



