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 the strong central and lateral denticles. They all liave 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 shalo over Coal No. 5, Mineral Point, Tuscara- 

 was Co., Ohio. 



CLADODrs 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 3i- 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, stride 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 Cladodics, the external pair are longer than the intermediate 

 ones, and Agassiz, in his description of the genus [Poissoiis Fossiles, 

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

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

 ever, that Cladodus of the Devonian and Carboniferous, is represented by 

 Hyhodus 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 difiicult to resist the conclusion that the relationship which 

 they hold to each other is a genetic one ; in other words, tiiat Hyhodvs is 

 descended from Cladodus.* 



The rule given by Aga.ssiz for distinguishing these genera is, however, 

 of such general application, that it seems hardly necessary lo 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 Hybodm in the Coal Measures of Northumberland and 

 Staffordshire, England, 



