DEVONIAN FISHES OF IOWA 137 



development of dental plates, its relations to contemporary 

 types being closely paralleled by Rhinochimaera among recent 

 genera.* There is excellent, reason for believing that the fin- 

 spines known as Heteracanthus or " Gamphacanthus " are truly 

 referable to the species under discussion, their size being com- 

 mensurate, and though not actually associated with the denti- 

 tion in any instance thus far reported, they invariably accom- 

 pany it in the Middle Devonian of Wisconsin and Iowa. Other 

 accompanying remains will be noticed later under a separate 

 heading. 



Formation and locality. Hamilton limestone; Milwaukee, 

 Wisconsin. Cedar Valley limestone; Waverly and Waterloo, 

 Iowa. State Quarry beds (Upper Devonian) ; North Liberty, 

 Iowa. 



Ptyctodus eastmani Weller. 



1906. Ptyctodus eastmani S. Weller, Trans. Acad. Sci. St. Louis 16, p. 462, pi. 

 1, figs. 31, 32. 



The geological occurrence of this species is interesting as indi- 

 cating the survival of a characteristic Devonian genus as late as 

 the dawn of the Carboniferous. Its presence in the Kinderhook 

 is paralleled by the persistence of Rhynchodus in the basal por- 

 tion of the Waverly in Boyle county, Kentucky. The distin- 

 guishing features of this species are given in the original de- 

 scription as follows : 



"Occasional abraded tritors of a species of Ptyctodus occur 

 in the Glen Park limestone, and one nearly perfect specimen of 

 a complete dental plate has been observed. . . . The most 

 notable characteristic of the Glen Park species as distinguished 

 from P. calceolus, is in the lower margin of the tooth, this mar- 

 gin describing a continuous slightly concave curve from the 

 posterior to the anterior extremity, while in P. calceolus this 

 margin is convex from the posterior extremity to a conspicuous 

 sinus below the anterior extremity of the tritor, and then con- 

 vex again nearly to the anterior extremity of the symphysial 

 beak where there is a conspicuous downward extension of the 

 tooth. The upper [=oral] surface also differs from P. calceolus 

 in having a less conspicuous differentiation between the tritoral 

 and the symphysial regions." 



*Garman, S., Chimaeroids, especially Khinochimaera and its Allies. Bull. Mus. 

 Comp. Zool. 1906, 41, p. 246.— Dean, B., Loc. cit. p. 128. 



