152 PALAEONTOLOGY OF ILLINOIS. 



anterior border, broadly rounded with a slight sigrnoidal curvature 

 on nearing the slightly produced posterior angle of the alation; 

 postero-lateral border gradually converging toward the outer margin 

 and bordered by a rather strong fold of the coronal enamel. Crown 

 broadly arched over the principal ridge, which occupies two-thirds 

 or more of the entire area, posteriorly rapidly sloping into the de- 

 pression on that side, whieh is bordered by the relatively narrow, 

 slightly upraised alate expansion. The surface is interrupted by 

 transverse sulci, especially noticeable near the border in the ante- 

 rior slope and in the posterior depression, and minutely and uni- 

 formly punctate. A worn specimen of ordinary size measures in 

 length along the antero-lateral border about 7 mm. ; greatest breadth 

 across inner margin, 8 mm. 



Maxillary posterior teeth trigonal in outline, strongly arched and 

 spirally inrolled. Antero-lateral border describing a gentle sigmoidal 

 curvature, basal portion channeled and well denned from the strongly 

 inbeveled coronal fold, which constitutes about one-third the height 

 of the border; postero-lateral border gently arched, approaching 

 point of inrollment at an angle of about 70 with the opposite side, 

 relatively deep, basal portion slightly inbeveled to the inferior edge 

 and faintly channeled, enamel fold relatively wide and sharply 

 rounded above, inbeveled below; inner margin making an angle of 

 about 30 with the anterior border, the anterior half very obliquely 

 produced backward from the very obtuse anterior angle, rounded 

 and sharply deflected at the inner angle or base of the coronal 

 ridge nearly at righk angles to the anterior course, with a slightly 

 concave curvature in passing the posterior depression to the posterior 

 angle, worn specimens showing the usual inbeveled inferior edge. 

 Coronal contour strongly marked, principal ridge culminating in the 

 rounded crest a little anterior of the longitudinal median line; 

 anterior slope steep, slightly depressed near the articular border, 

 where it flares out into a narrow border fold ; posterior slope regu- 

 larly descending with moderate concavity, and merging into the 

 posterior depressed belt, which is bordered by the narrow and but 

 slightly upraised expansion of the alate posterior border. Besides 

 the irregularly elongated pores, the surface is marked by transverse 

 sulci and intervening wider ridges in the same manner noticed in the 

 mandibular teeth. A mature, perfect tooth measures across the 

 inner margin 9 mm. ; length along antero-lateral border to the in- 

 rolled outer margin, 7 mm. ; length along coronal axis, 13 mm. 



