DEVONIC FISHES OF THE NEW YORK FORMATIONS 75 



Homacanthus acinaciformis Eastman 



Plate I, figure 16 



1903 Homacanthus acinaciformis C. R. East/nan. Mus. Comp. Zool. Bui. 

 39:218, pi. 5, fig. 58 



Spines comparatively small, slender, gradually tapering, gently and 

 uniformly arched ; lateral surface with five or six continuous longitudinal 

 ridges ; posterior denticles slender, rather widely spaced. 



The small spines known under this designation are more strongly 

 curved than those found in the Lower Carbonic limestone, but according 

 to J. W. Davis, there is considerable variation in this respect, even amongst 

 spines belonging to a single species. Some resemblance is to be noticed 

 between the present form and the Upper Devonic spines from Ohio 

 described asHoplonchus parvulus by Newberry. 



Formation and locality. Chemung group ; Warren, Pa. 



Genus ctenacanthus Agassiz 



Dorsal fin spines robust, often attaining a large size, laterally com- 

 pressed ; sides of exserted portion ornamented with longitudinal ridges, 

 usually crenulated or denticulated, rarely smooth ; posterior face flat or 

 concave, with a series of small denticles upon each margin. 



It is certain that spines of this character were possessed by sharks of 

 more than one genus. Reference has already been made to the occurrence 

 of these defenses in Cladoselache, and Newberry was strongly inclined to 

 suspect, from a discovery in the Waverly of Ohio,' that Ctenacanthus and 

 Orodus may be synonymous. Of primary importance in the distinction of 

 species is the general conformation of the spines, especially their curvature, 

 form of cross-section, and length of inserted portion. Next in order are to 

 be considered the number, shape and direction of the longitudinal costae, 

 with the special ornamentation of the same ; and still further distinctive 

 characters are to be found in the nature of the posterior face and anterior 

 margin, or "cutwater." A class of spines agreeing in their abbreviate, 



' O. Geol. Sur. Rep't 1874. v. 2, pt 2, p. 54. 



