118 PALEONTOLOGY OF ILLINOIS. 



line uniting the inner, anterior and posterior angles, basal portion 

 channeled, coronal enamel forming a narrow inbeveled fold along 

 the upper edge; postero-lateral border very oblique, forming an 

 angle of 40 to 50 with the opposite border, in respect to basal 

 portion and shallow enamel fold, presenting the usual generic char- 

 acteristics ; inner margin strongly arched from the subacute posterior 

 extremity round the base of the posterior lobe, in front of which it 

 forms a rather deep broad sinus, and again broadly arched in pass- 

 ing the anterior coronal prominence to the obtuse anterior angle. 

 Coronal region nearly centrally divided by the median depression ; 

 posterior lobe prominent, anterior face steeply rising into the 

 rounded crest, whence the broader slope more gradually and regu- 

 larly descends with slight transverse convexity to the postero- 

 lateral border, just above which lies a faint depressed parallel belt ; 

 median depression occupying less than one-fourth the lateral area 

 of the surface, rather deeply excavated and usually well defined; 

 crest of anterior lobe near the posterior side, the broad slope de- 

 scending in regular convexity to the antero-lateral border. Sur- 

 face marked by transverse rugae or imbrications over the less 

 abraded portion of the posterior lobe, and which on reaching the 

 median depression are, in some instances, rather strongly deflected 

 from a direct course downwards and forward, becoming obsolete in 

 the region of the anterior lobe, which is occupied by irregular prom- 

 inences, producing an elegant verrucose ornamentation, irregular 

 ridges sometimes taking the place of the verrucose prominences ; 

 surface punctse fine, spaced by little more than their own diameter. 

 A mature specimen measures in greatest diameter between the inner 

 angles 40 mm. ; length of antero-lateral border to point of inroll- 

 ment about 15 mm. 



Mandibular posterior teeth sub-trapezoidal in outline, strongly 

 arched and inrolled. Antero-lateral border moderately oblique in 

 its outward and forward course from the very obtuse inner angle, 

 channeled and limited above by the narrow enameled fold ; postero- 

 lateral border converging toward point of inrollment at an angle of 

 50, or less, with the inner margin presenting the usual channeled 

 condition and enamel fold above ; inner margin strongly arched 

 round the base of the median ridge, with a broad concave curva- 

 ture behind in passing into the produced subacute posterior extremity. 

 Median lobe of crown culminating in a sharply rounded crest, 

 anterior of a line through the centre of the tooth, steeply sloping 

 and merging into the moderately depressed anterior belt, the oppo- 



