124 PALEONTOLOGY OF ILLINOIS. 







a triturating surface interrupted by prominent transverse ridges and 

 intervening deep furrows, corresponding to the coronal crests of the 

 individuals of the series ; in some instances the individual teeth are 

 so intimately united along the impingement of their bases as to 

 obliterate all trace of suture ; again, in other examples the original 

 or occasional individuality of the teeth is indicated by a faint 

 suture, extending in from the borders of the series, while others 

 again show the complete series in natural successional order, but 

 with their bases free. The individuals of the series regularly 

 diminish in size from within outward, although the tooth of the 

 inner margin sometimes presents an immature coronal crest, adher- 

 ing to the inner basal declivity of the immediately preceding fully 

 developed tooth, a feature known to obtain in the Helodus-like teeth 

 associated with Chitonodus latus, e. g. Helodus consolidatus, N. and 

 W. The independent teeth are distinguished by [their long-elliptical 

 transverse outline seen from above, slightly arched backward along 

 the inner margin of the crown, the opposite side being protuberant 

 in the middle, with concave curvature towards the extremities. The 

 crown rises into a tumid eccentric apex nearer the postero-lateral ( ?) 

 extremity, outer face slightly concave, opposite side moderately con- 

 vex, sharply inbeveled and defined from the base, the extremities 

 marked by a sort of enamel fold, which also faintly appears along 

 the outer margin, but destitute of imbrications, such as appear in 

 the coronal belt of Chomatodus. The base is relatively shallow, 

 inbeveled in front, more or less channeled and irregularly coarsely 

 pitted, inner margin much produced outward and downward to the 

 dull inferior edge, vertically coarsely rugose ; inferior surface faintly 

 depressed, smooth. The large tooth of a medium-size series of 

 three firmly coalescent individuals measures in lateral diameter of 

 crown 6 mm., diameter at the middle 2 mm. ; greatest height of 

 crown 1 mm. Crown originally enveloped in a dense semi-opaque 

 enamel, the worn surface showing rather widely spaced puncta3, 

 varying, however, considerably in the latter respect. The associated 

 teeth clearly homologous with the present form, present rather a 

 wide range in variation, particularly in respect to the contour of 

 the coronal region. In some of the teeth the crown is much de- 

 pressed; in others, again, the outer face presents a wide, plain, 

 elliptic area, the inner slope very low, and the crest crowded over 

 past the basal border, in which condition it resembles certain forms 

 of Tanaodus, although the base is entirely different from that of the 

 latter genus. 



