226 PALEONTOLOGY OF ILLINOIS. 



tical articular wall, which latter shows a slight concavity between 

 the angles, the anterior angle distinctly truncated for the narrow 

 oblique articular facet. Anterior and posterior margins parallel, 

 nearly straight, or gently arched forward with a slight concavity 

 toward the inner angle in front, and a corresponding convexity in 

 the posterior margin, inbeveled to the basal portion, which was of 

 proportionate vertical depth. The basal support of the borders is 

 not preserved. The surface of unworn teeth exhibits an exceedingly 

 intricate reticulated ornamentation, produced by the rugre occupying 

 the interspaces between the punctse, the prevalent continuity having 

 a transverse direction; on the other hand, worn surfaces show 

 rather coarse, crowded punctse, confluent in the depressed transverse 

 belts. Lateral diameter of a medium-size smooth tooth across the 

 posterior margin, 37 mm. ; length along inner border, 22 mm. ; 

 depth of tooth, at least 8 mm. 



Professor Worthen has obtained from the same deposits, and 

 associated with the foregoing teeth, a single imperfect example of a 

 tooth which may prove to be identical with the opposed mandibular 

 form of the present species. It shows a medium size tooth, quadri- 

 lateral in outline, the worn anterior margin slightly arcuate, though 

 originally probably gently arched, corresponding approximately with 

 the moderate concavity of the posterior margin, inner border making 

 nearly a right-angle with the margins, posterior angle truncated, 

 with a rather prominent angulation about one-third the distance 

 forward ; outer border unknown. The crown is well defined all 

 round from the deep, slightly excavated basal walls, which are in- 

 beveled strongly so along the anterior margin. The latter feature 

 accords with the rather marked convexity of the coronal region from 

 behind forward, giving to the series of teeth a strongly rolled longi- 

 tudinal section, the surface showing a faint transverse furrow in the 

 anterior half, where, as also in the slope bordering the posterior 

 margin, the surface presents the same rugose ornamentation de- 

 scribed in connection with the previously mentioned form, the more 

 exposed parts showing a smooth, densely punctate surface. The 

 coronal area is nearly plane, or faintly depressed transversely, with 

 a slight depression parallel with the outer border, and showing a 

 fullness somewhat contrasting with the opposed maxillary form. 

 Transverse diameter at the posterior margin, at least 40 mm. ; length 

 of inner border, 22 mm.; vertical depth of tooth, at least 10 mm. 



While the previously noticed maxillary form hardly requires de- 

 tail comparison with the homologous form of Psammodus 



