58 PALAEONTOLOGY OF OHIO. 



Ge^us PLATYODUS (nov.gen.). 



Teetli elliptical in outline, crown slightly arched in both directions, 

 surface punctate in undulate lines, but without folds or ridges. 



J^othing is known of this genus except what is taught by a single speci- 

 men, which forms the basis of the specific description given below. 



It is evident that it was once worn by an ancient Elasmobranch fish al- 

 lied to Deltodus, Sandalodus, etc., but distinctly separated from them by 

 its rounded outline, simple margin, low, evenly-arched crown, and linear 

 punctation. How many teeth were borne on the jaws, and how much 

 varied in form they were, if more than two, will doubtless be determined 

 by future discoveries. 



PlATYODUS LIISTEATUS (n. Sp.). 

 Plate LIX., Fig. 12. 



Teeth broad and low, ovojd or elliptical in outline, 3 inches long by 

 14- inches Avide ; crown surface gently arched in both directions, punctate 

 throughout, punctations arranged in broadly undulate lines which cross 

 the crown transversely. 



The only tooth of this iish yet known was found by the writer in the 

 Waverly shales, on the farm of Mr. Dunn, eight miles south of Liberty, 

 Casey Comity, Ky. It is somewhat worn by use, and corroded by expos- 

 ure, but still exhibits cliaracters by which it may be distinguished, at a 

 glance, from any other heretofore described. Of these characters the 

 most conspicuous are its great size, low, doubly-arched crown, without 

 ridges or furrows, and the undulate lines o-f punctse wdiicli occupy all the 

 surface, 



HOLOCEPHALI. 



CHIM^ROIBL 

 Genus RHYNCHODUS, Newb. 



The announcement made in our first volume that the remains of Chi- 

 mseroid fishes had been discovered in the Devonian rocks of Ohio, and the 

 reference of the genus RhyneJiodus to this family, may have excited some 

 surprise and perhaps incredulity, as Chimseroids had not before been 



