76 NEW YORK STATE MUSEUM 



Stumpy proportions, and inserted very obliquely in the integument, is prob- 

 ably to be correlated with the posterior dorsal fin. They contrast strongly 

 with the group of slender, elongated and tapering spines which were 

 undoubtedly situated in advance of the first dorsal fin.' 



Ctenacanthus wrighti Newberry 

 1884 Ctenacanthus wrighti /. S. Newberry. N. Y. State Mus. 3Sth Rep't, 



p. 206, pi. 16, fig. 12-14 

 1889 Ctenacanthus wrighti J. S. Newberry. U. S. Gaol. Sur. Monogr. 16: 66, 



pi. 26, fig. 4 

 An examination of the peculiarly shaped and unusually large fin spine 

 upon which this species is founded, now preserved in the American Museum 

 of Natural History in New York, has served to confirm the correctness at 

 all points of Newberry's description, which is as follows : 



Spine of large size, long triangular in outline ; anterior margin 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, becoming 

 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 to have been abso- 

 lutely straight from base to summit. Along the line of junction between 

 the enameled and burled portions the spine must have been 2 Inches wide, 

 but it tapered rapidly upward, terminating in a slender, acute point. The 

 exposed surface Is more completely covered with ridges similar In charracter, 

 and the pectination is more crowded than in any other species known to me. 

 In its broad base and its general and uniform ornamentation this spine has 

 some resemblance to C. s p e c i o s u s St J. & W., specimens of which have 

 been in my hands, but the line of demarcation between the ornamented and 

 buried portions Is less oblique, showing that the spine was more erect [and 

 hence referable to the anterior dorsal fin] ; the ridges are considerably 

 coarser and the form is straighten- The pectination Is also less oblique and 

 closer, compared with the coarseness of the ridges. 



Formation and locality. Hamilton limestone (Erian), " near the middle 



of the Moscow shale ; Cashong creek, Yates county, N. Y.'' 



'Science, n. s. 1901. 14: 795. 



