122 PALEONTOLOGY OF ILLINOIS. 



Mandibular median teeth sub-triangular in outline. Postero- 

 lateral border slightly curved sigmoidally in conformity with the 

 anterior articular border of the posterior terminal tooth, basal 

 portion rather deeply channeled and coarsely pitted, forming the 

 greater part of the height of the border, well-defined from the 

 enamel-fold and terminating below in a thin outward produced 

 rim; antero-lateral border converging toward outer extremity at an 

 angle of about 30 with the opposite border, relatively short, simi- 

 larly channeled and pitted as mentioned in connection with the 

 posterior border; inner margin making a marked sigmoidal curva- 

 ture, broadly rounded in passing the base of the coronal promi- 

 nence, and thence curved outward on approaching the obtuse 

 anterior angle, joining the posterior border nearly at a right angle. 

 Coronal contour presenting a simple median ridge, the posterior 

 slope slightly arched transversely and gently descending to the 

 postero-lateral border, which is occupied by an abruptly beveled 

 slightly depressed belt margined by a narrow, minutely crenulated 

 fold distinctly defining the coronal and basal portions, worn indi- 

 viduals showing a more or less rounded edge; the opposite slope 

 declines more abruptly into a shallow depressed belt occupying the 

 anterior surface, bordered by the narrow alation, over the edge of 

 which the enamel makes a regularly rounded fold sharply defined 

 along the strongly inbeveled margin from the basal portion ; along 

 the inner margin the coronal region is defined by a narrow rounded 

 fold inbeveled to the deep basal belt, which extends downward into 

 a thin edge corresponding with that of the posterior tooth. Super- 

 ficial enamel and punctate structure the same as described in 

 connection with the preceding form. Length along postero-lateral 

 border 10 mm,; greatest breadth between the inner angles 9 mm.; 

 length of antero-lateral border to point of inrollment 6 mm. 



Ultimate teeth occupying the dentigerous extremity of the lower 

 jaw unknown. 



Maxillary posterior teeth (Streblodus, Agass.) subspatulate in gen- 

 eral outline, strongly and regularly arched from within outward. 

 Antero-lateral border with slight forward obliquity to the long axis 

 of the tooth and gently curved sigmoidally, basal portion channeled 

 and extending downward and outward into a thin rim, coarsely 

 pitted; postero-lateral border broadly arched in a slight sigmoidal 

 curvature, converging toward inrolled outer margin at the angle of 

 55 to 65 with the opposite side, basal portion apparently relatively 

 low, channeled, and posteriorly expanding beyond the coronal limit 



