46 PALEONTOLOGY OF OHIO. 



anterior and posterior faces strongly striated. Lateral denticles four, the 

 outer pair largest, all conical, acute and striated. Base elliptical in out- 

 line, thin and sharp-edged. 



The most distinctive character of this species is the extreme sharpness 

 of tlie strong central and lateral denticles. They all have a nearly circu- 

 lar section, and are distinctly striated ; at their summits they are drawn 

 out into line points more elongated and acute than in any other equally 

 large species with which I am acquainted. 



Formation and Locality : Bituminous shaln over Coal No. 5, Mineral Point, Tuscara- 

 was Co., Ohio. 



Cladodus Hertzeri (n. sp.). 



Plate LVIII., Figs. 5, 5 a. 



Teeth broader than high, massive and strong ; base semi-elliptical in 

 outline, 7 lines long by 3^ lines wide ; central cone 6 lines high, robust, 

 conical, subacute, with a circular section, considerably inclined back- 

 ward ; lateral denticles, two pairs, the interior pair more than half as 

 large as the central cone, outer pair much smaller ; both central and lat- 

 eral cones rather finely striated, strias strongest on posterior face and 

 sides. 



The most striking peculiarities of this remarkable species, are the breadth 

 of the base, which exceeds the height of the central cone, and the re- 

 versed and abnormal inequality in the size of the lateral denticles. In most 

 species of Cladodus, the external pair are longer than the intermediate 

 ones, and Agassiz, in his description of the genus {Poissons Fossiles, 

 Tome III., p. 196) makes this a diagnostic cliaracter, and that by which 

 he distinguishes Cladodus from Hyiodus. There is little doubt, how- 

 ever, that Cladod^bs of the Devonian and Carboniferous, is represented by 

 Hybodus in the Mesozoic rocks. The two genera shade into each other 

 in such a way that it is impossible to draw any sharply-defined line between 

 them, and it is difficult to resist the conclusion that the relationship wliich 

 they hold to each other is a genetic one ; in other words, that Hylodus is 

 descended from Cladodus* 



The rule given by Agassiz for distinguishing these genera is, however, 

 of such general application, that it seems hardly necessary to modify it, 

 further than to report some exceptions to it. 



*Mr. W. J. Barkas, in a paper published in the Geological Magazine of April, 1874, 

 claims to have discovered true Hybodus in the Coal Measures of Northumberland and 

 StafEordshire, England. 



