YEBTEBBATES. 307 



giving rise to the prominent lateral convexity in the coronal contour, 

 and bordered by. a rather, wide coronal belt composed of at least two 

 imbricating folds. The coronal surfaces are usually smooth, in worn 

 surfaces coarsely striato-punctate, and sometimes enlarged iu a dense, 

 vertically undulated or corrugated enamel layer. Base strong, thick, 

 rectangular in shape, in depth nearly equal to the hight of the crown, 

 somewhat less in lateral diameter, slightly compressed in the middle 

 and expanded below, inferior surface well-detiued and beveled from the 

 convex to the concave border, slightly produced beyoud the vertical 

 plane of the convex crown-face, and sharply defined above by the pro- 

 jecting basal angles of the crown. A specimen of ordinary dimensions 

 measures in lateral diameter of crown .12 inch, hight of convex crown- 

 face .06, hight of concave face .10, lateral diameter of base .08, entire 

 elevation of tooth .14 inch. 



Although we have seen but few examples of this exceedingly small and 

 handsome form in the collection of Mr. Van Horne, their state of preser- 

 vation, fortunately, is such as to render their distinctive features easily 

 discernible. It is most intimately related to L. serratus of the Upper 

 Burlington limestone ; but, besides being scarcely half the size of that 

 form, it is further distinguished by the relatively larger root, the verti- 

 cal position of the convex crown-face and its nearly horizontal basal 

 line, while that of the opposite face is more strongly and regularly 

 arched downward, also the inequal elevation of the coronal faces; the 

 denticulations of the crest are more remote from the apex. 



Position and locality : Upper beds of the St. Louis limestone ; Alton, 

 Illinois ; St. Louis, Missouri. 



Genus TANAODTIS, St. J. and W. 



In recognizing the generic distinctness of the group of teeth embraced 

 under the above designation, we have not been Jed to such disposi- 

 tion by the assumption, if Antliodus differs generically from Petalodus, 

 so Chomatodus in like manner differs from the present group; but it has 

 rather been with the hope of eliminating from the heterogeneous assem- 

 blage of forms usually referred to Chomatodus such well-characterized 

 groups which have an equal value as distinctive expressions with the 

 various groups already recognized, which constitute the family of Petal- 

 odonts. In the present instance we have a peculiar expression of char- 

 acteristics which pertain to certain individuals or forms which extend 

 through a considerable time-space in the Carboniferous period — indeed, 

 appearing early iu the period and continuing to the close of the Upper 

 Coal Measure epoch. And these peculiarities, as compared with what 

 may be regarded as typical of Chomatodus in the restrictive sense here 



