128 PALEONTOLOGY OF ILLINOIS. 



the usual channeled and downward and outward projecting basal 

 rim which is coarsely pitted, the border having a course slightly 

 oblique outward and forward to the transverse axis of the tooth; 

 postero-lateral border converging toward the outer margin at an angle 

 of about 60, basal portion channeled and somewhat produced be- 

 yond the coronal limits towards the posterior extremity ; inner mar- 

 gin broadly arched round the base of the principal coronal ridge, 

 with a short concavity in front and a broader one in passing the 

 posterior depression into the alate, subacute angle, worn specimens 

 showing the usual inbeveled edge. Anterior belt of crown well-de- 

 fined, narrow, slightly convex transversely, the coronal enamel fold- 

 ing over the antero-lateral border in a narrow inbeveled belt dis- 

 tinctly defined from the basal portion; median ridge prominent, 

 relatively broad, occupying considerably more than half the trans- 

 verse diameter of the crown, moderately and regularly arched trans- 

 versely and well-defined on either side by an obtuse angulation or 

 furrow separating it from the anterior belt and the posterior depres- 

 sion ; posterior alation relatively narrow, considerably upraised, 

 nearly plane transversely, the coronal enamel forming a delicate 

 inbeveled fold along the outer edge. Surface minutely punctate, the 

 medullary tubes somewhat widely spaced and about thirty occurring 

 within a square millimetre, and disposed in scroll-like curves over 

 the surface of the tooth. Length of a medium-size tooth along the 

 antero-lateral border 8 mm ; breadth between angles of inner margin 

 13 mm ; breadth of median lobe at inner margin 8 mm ; do. of pos- 

 terior alation 3 mm ; do. anterior belt 2 mm. 



Mandibular median form, of which the collections offer a solitary 

 imperfect example showing about half the inner portion of a mature 

 tooth, exhibits a moderately elevated, sub- angular median ridge, a 

 narrow concavity bordering the postero-lateral edge over which the 

 enamel forms a narrow inbeveled fold distinctly defined from the 

 channeled basal portion ; slope in front slightly concave transversely 

 on nearing the antero-lateral border, which latter, as also the very 

 oblique inner margin, is mutilated and not clearly defined. Surface 

 punctation similar to that observed in the posterior terminal form. 



Maxillary posterior teeth subspatulate in general outline, strongly 

 inrolled. Antero-lateral border slightly oblique with a gentle con- 

 cave curvature outward and forward from the obtuse inner angle ; 

 postero-lateral border diverging at an angle of 26, more or less, 

 with the opposite border, presenting a broad gentle curvature between 



