88 PALAEONTOLOGY OF ILLINOIS. 



2, 2«, a broader specimen, with but two crowns, upper and lower surfaces, from 

 Warsaw, Illinois. 



Formation and locality: Keokuk limestone, St. Francisville, Missouri, and 

 Warsaw, Illinois. 



Helodus (Cochliodus) nobilis, N. and W. 



PI. VI, Pigs. 3-6. 



Teeth forming a series of six, diminishing from before back- 

 ward,; set upon a segment of a circle; the anterior one large 

 and strong, sub-elliptical in outline ; the extremities rounded 

 or blunt-pointed. Crown conical in profile, with a sub-median, 

 prominent, ripple-like cone, underneath which is a deep sinus 

 filled by the root ; enameled surface, uniformly, rather finely 

 punctate throughout. Root as high and as broad as the crown; 

 anterior face nearly vertical, vermicularly roughened; posterior 

 face higher than anterior, oblique. The smaller teeth of the 

 series are similar in form to the largest, but having the median 

 cone less worn and more pointed. 



There can scarcely be a doubt that these teeth occupied the central portion 

 of the jaw, in two or more rows, between the large convoluted teeth which we 

 have described under the name of Cochliodus nobilis. This is indicated, and 

 we may almost say proven, by the fact that the specimens figured plate VI, 

 figures 4-6, and plate VII, figures 1, 2, 4, were found impacted together — disar- 

 ranged, but in contact — and with some traces of the cartilaginous jaw upon 

 which they were once set. The character of the microscopic structure of the 

 crown surfaces is precisely the same in both, as is their color. Whether the 

 entire dental series was procured or whether a portion was lost wo have no 

 means, at present, of determining, but the convoluted teeth seem to have been 

 derived from both the upper and lower jaws. There are also many more of the 

 conical ones than the series represented in our figure. Whether these former 

 numerous medial rows were on a single jaw, or were common to both, is as yet 

 undeterminable. As has been before remarked, a want of symmetry of these 

 Helodoid teeth seems to prove that there was more than one row on one, per- 

 haps both of the jaws. 



Figures 3, 3 a, 36, give side and top views and profile section of a large 

 detached tooth. Figures 4, 46, represent one of the series we have described, 



