DEVONIAN FISHES OF IOWA 107 



intermediate denticles in the angles between the principal cusps. 

 Extremities of outer cusps slightly divergent. 



These minute teeth are accompanied in the same formation 

 by others of about the same size, but having the coronal cusps 

 apparently smooth. Although regarded provisionally as per- 

 taining to a distinct species, named P. sophiae by Messrs. St. 

 John and Worthen, the authors admit the possibility of the two 

 forms representing the upper and lower dentition respectively 

 of one and the same species. Only one specimen has been figured 

 of the smooth form designated as P. sophiae, and none have 

 come under the observation of the present writer. But for the 

 fact that the base is well denned, these minute teeth might readily 

 be mistaken for Conodonts. 



Formation and locality. Cedar Valley limestone; Waterloo, 

 Iowa. 



Family CL4DODONTIDAE. 



An indefinable family, apparently closely related to the Pleu- 

 racanthidae. 



Genus CLADOOUS Agassiz. 



This typically Lower Carboniferous genus occurs sparingly 

 in the Upper Devonian, and only two instances are known of its 

 representation in the Middle Devonian, the species noticed im- 

 mediately hereafter being found in the Columbus limestone 

 (Ulsterian) of Ohio, and the next following in the Hamilton of 

 Milwaukee, Wisconsin. It is quite possible that some detached 

 teeth of similar nature which range upward into the Carbon- 

 iferous belong in reality to Pleuracanthid sharks, whose earliest 

 appearance is perhaps indicated by forms like Protodus and 

 Doliodus in the Lower Devonian. Cladodont sharks of the Lower 

 Carboniferous were apparently spineless, and in this respect 

 differ from the spiniferous Cladoselache of the Upper Devonian 

 and Waverly. 



