90 PALEONTOLOGY OF ILLINOIS. 



rounded or sigmoidally curved from the obtuse anterior angle into 

 the more acute extremity of the posterior wing. Coronal contour 

 presenting three divisions, all regularly narrowing toward the outer 

 extremity, viz : In front, a narrow transversely plane belt ; a more 

 or less prominent median ridge denned in front by a slight angula- 

 tion from the anterior belt, and sloping posteriorly into the broad 

 depression from which rises the more or less laterally expanded 

 posterior wing, well preserved teeth also showing a slight angula- 

 tion on this side of the median lobe where it joins the posterior 

 depression. 



Posterior teeth of the upper jaw subspatulate in general outline, 

 terminating posteriorly in an acute angle or spur, antero-lateral 

 border truncated generally obliquely outward and backward, strongly 

 inrolled along the outer margin for two-thirds the distance from the 

 anterior extremity. Crown defined from the base by a shallow in- 

 beveled fold along both the antero and the postero lateral borders, 

 the basal portion in front nearly vertical or somewhat channeled, 

 projecting downward and outward behind where it forms the spur 

 at the extreme posterior angle. Coronal region showing a depressed 

 posterior prominence, in front of which less or more remote, a 

 smaller secondary ridge, separated by a plain intervening furrow, 

 and having an oblique course from the within outward in conformity 

 with the direction of inrollment ; anterior neck generally smooth, 

 destitute of marked revolving ridges or furrows, and gradually con- 

 tracting toward the truncate anterior border, where the vertical 

 depth of the tooth is at the minimum, in consequence of which the 

 anterior border is extremely liable to mutilation as is shown by the 

 rarity of entire examples of this form. 



The maxillary posterior form is immediately succeeded in front by 

 at least one series of teeth, consisting of transverse coronal ridges, 

 which together present a trapezoidal outline, the postero-lateral bor- 

 der articulating with the posterior tooth nearly straight and forming 

 a right or obtuse angle with the inner margin, antero-lateral border 

 more or less obliquely converging towards the outward extremity. The 

 coronal ridges present a series of parallel crosts, vertically convex 

 behind and concave in front, which in general possess to some 

 extent characters in common with certain forms of teeth, which have 

 been variously referred to the genera Hclodus arid Chomatidus. 



Coronal surface presenting the usual enamel coating; worn sur- 

 faces punctate. 



