91 PALEONTOLOGY OF ILLINOIS. 



posterior angle, and marked above by the narrow enameled fold which 

 is defined from the basal portion by a slight channel ; antero-lateral 

 border forming a vertical face at the inner angle, gradually sloping 

 upward and backward toward the outer extremity, and, save a nar- 

 row belt along the inferior edge, enveloped in the enamel fold, which 

 is also well defined from the. basal rim. Coronal region traversed 

 longitudinally by a moderately prominent, transversely arched median 

 ridge, the axis of which lies nearest the antero-lateral border, and 

 sharply defined on either side by an angulation or narrow .groove ; 

 anterior belt relatively narrow, very faintly arched transversely, or 

 nearly plane, and scarcely half the width of the median-lobe ; pos- 

 terior alation about the same width as the median-lobe, transversely 

 concave and merged into the posterior depression from which it 

 steeply rises into the produced posterior angle. Surface finely punc- 

 tate. Greatest length of tooth along postero-lateral border, 40 mm. ; 

 ditto, antero-lateral border, 30 mm. ; breadth across inner margin, 

 23 mm. ; greatest height of antero-lateral border, 8 mm. 



Maxillary posterior teeth subspatulate in outline, strongly from 

 within outwards, outer margin strongly inrolled ; postero-lateral 

 border making a broad curve outward and forward from the obtusely 

 pointed posterior angle to point of inrollment, thence to the anterior 

 angle the outline is slightly concave; inner margin arched round 

 the base of the coronal prominence, and thence nearly straight to 

 the anterior border ; antero-lateral border slightly obliquely truncated 

 from the inner to the outer angle, and equal to about two-thirds the 

 diameter of the tooth along a line diagonal to the direction of inroll- 

 ment across the posterior ridge. Posterior lobe of the crown occu- 

 pying little more than one-third the total breadth of the tooth, 

 moderately arched transversely, the crest culminating in front where 

 the surface rapidly descends into the narrow furrow defining it from 

 the subordinate ridge, which latter presents a nearly uniform con- 

 vexity, gradually narrowing from within outward, and, in perfect 

 specimens, defined in front by a distinct though slight angulation; 

 anterior neck nearly smooth, with a few obscure rugose lines along 

 the inner margin, destitute of revolving ridges. Breadth of a medium- 

 size tooth between the inner angles, 48 mm. ; breadth of tooth across 

 the posterior prominence diagonal to the inrollment, 20 mm. ; length 

 along antero-lateral borders, 13 mm. 



Maxillary median teeth forming a triangular plate articulating 

 with the posterior tooth by the straight postero-lateral border, the 



