GENUS PSEPHOBUS, Agassiz. 



Psepkodus, Agassiz, MSS., 1859, etc. 



The genus Psephodus was recognized by Professor Agassiz iu 1859, 

 by whom Cochliodus ma-gnus, Ag., of the Irish Mountain limestone, 

 was regarded as the typical species. This determination was 

 accepted by British palseichthyologists, and a few years later, 1862, 

 it was authoritatively published by Messrs. J. Morris and G. E. Rob- 

 erts, in the Quat. Journ. of the Geol. Soc. of London, XVIII, p. 

 102. At a subsequent date, 1866, Messrs. Newberry and Worthen, 

 in their investigations of the fossil fishes published in the report of the 

 Illinois Geological Survey, Vol. 2, p. 92, described several congeneric 

 species from the American Lower Carboniferous formations, however, 

 evidently overlooking the prior published conclusions arrived at by 

 Professor Agassiz, as they distinctly identify the type species of 

 Psephodus with the American species, to which they applied the gen- 

 eric designation Aspidodus. In regard to the generic identity of the 

 American species described under the latter designation, as also 

 those additional ones herein first made known, with Psephodus mag- 

 nus, Agass., there is not the least doubt. 



In the present work the results of the attempts made to identify 

 the probable complete dentition of Psephodus are omitted, only such 

 forms receiving brief diagnostic notice, the relations of which may be 

 considered as even more than probably determined. These consist 

 of two distinct forms of heavy, more or less spirally in-rolled trit- 

 urating or crushing plates, investing the median region of the rami 

 of the jaws: 



