VERTEBRATES. 57 



Figures 17 and 17a represent a fragment of a worn tooth; basal surface and 

 section natural size. 



Formation and locality: Keokuk limestone, Warsaw, Illinois. 



Chomatodus multiplicatus, N. and W. 



PI. Ill, Figs. 18, 18a, 186. 



Teeth very broad and low, four times as broad as high; 

 posterior aspect showing three nearly equal parallel bands, the 

 crown, the basal folds and root; the posterior face of the crown 

 is linear in outline, rounded at either end, its upper and lower 

 borders nearly straight. The surface is smooth and polished, 

 the cutting edge acute and very finely crenulated by the fine 

 marginal striation of the anterior face; basal band of imbricated 

 folds turned up and slightly rounded at either end, projecting 

 beyond the crown, enamel folds numerous (7-8), flattened, the 

 upper ones slightly widest; anterior face of crown strongly 

 deflected backward, but little narrower than the posterior, 

 concave vertically, gently arched laterally, its superior border 

 beveled off to form the cutting edge, the beveled face being 

 very finely striated vertically; anterior basal ridge prominent, 

 narrow, showing about three folds; base smooth, narrow; root 

 as high and nearly as broad as the crown, quadrangular; its 

 posterior face retreating, its anterior and higher surface beveled 

 off from the middle down to an acute edge, everywhere rough- 

 ened and pierced by the foramina of the nutrient vessels; en- 

 tire height, 6 lines; breadth, 24 lines; height of crown, basal 

 folds, and root on posterior face, each 2 lines. 



It is to be regretted that this very interesting and distinct species is repre- 

 sented in the collection by a single specimen only. Its very unusual breadth 

 separates it widely from the typical Petalodi, and yet, in other respects, it is 

 apparently like them. This, in itself, however, would indicate peculiarities of 

 the dentition, at least of the size, form and arrangement of the teeth in the 

 jaws of the fish possessing them, which, if we could define it, would serve as a 

 satisfactory basis for the description of the genus. .It is but fair to suppose 



—8 



