DEVONIAN FISHES OF IOWA 153 



Ctenacanthus belonged to sharks having the dentition of Orodus, 

 in which case the two generic terms apply to one and the same 

 kind of fish. 



Of primary importance in the distinction of species is the 

 general conformation of the spines, especially their curvature, 

 nature of cross-section, and length of inserted portion. Next 

 in order of importance are the number, shape and direction of 

 the longitudinal costae, their mode of origin, whether by bi- 

 furcation or implantation, together with their finer ornamenta- 

 tion; and still further distinctive characters are to be found in 

 the nature of the posterior face and the sometimes keeled or 

 otherwise differentiated anterior margin, or "cutwater". A 

 class of spines agreeing in their short, stocky proportions, and 

 very oblique insertion in the integument, is probably to be cor- 

 related with the posterior dorsal fin. They contrast strongly 

 with the group of slender, elongated and tapering spines whose 

 position was undoubtedly in advance of the first dorsal fin.* 



Ctenacanthus wrighti Newberry. 



1884. Ctenacanthus wrighti J. S. Newberry, 35th Rept. N. Y. State Mus. p. 



206, pi. 16, figs. 12-14. 

 1889. Ctenacanthus wrighti J. S. Newberry, Monogr. U. S. Geol. Surv. 16, p. 



66, pi. 26, fig 4. 

 1907. Ctenacanthus wrighti C. R. Eastman, Mem. N. Y. State Mus. 10, p. 76. 



An examination of the peculiarly shaped and unusually large 

 fin-spine serving for the type of this species, now preserved in 

 the American Museum of Natural History in New York, con- 

 firms the entire accuracy of Newberry's description, which is 

 as follows : 



Spine of large size, long triangular in outline; anterior mar- 

 gin straight, laterally compressed ; medullary cavity large, open 

 posteriorly to the middle of the spine ; posterior face traversed 

 above by >a strong rounded ridge; [posterior] denticles small; 

 surface of exposed portion entirely covered with pectinated 

 ridges of nearly uniform width on the front and sides, becom- 

 ing narrower and less distinctly pectinated near the posterior 

 margin. 



The spines of this species are very striking in their characters 

 as regards both form and markings. The anterior margin seems 



* Science, n. s., 1901, 14, p. 795. 



