VERTEBRATES. 117 



have been overlooked. We infer, however, from the figures and descriptions 

 of Prof. McCoy, (British Palaeozoic Fossils, p. 633, pi. 3 G,figs. 13, 14 and 16,) 

 that the species which he calls Leptacanthus junceus and L. Jenkinsoni are 

 generically identical with ours ; the latter species being distinguishable from 

 that before us only by the less perfect regularity of costation near the base, 

 greater spacing of the denticles, and the striations of the surface — fair specific 

 differences. If, then, Prof. McCoy's carboniferous fin-spines are properly re- 

 ferred to Leptacanthus, ours should be so ; but for the reasons given above it 

 seems in some degree probable that the reference of his specimens to that genus 

 was unwarranted. The resemblance which the spines before us and those of 

 Prof. McCoy bear to some of the more slender and compressed forms, now in- 

 cluded in Ctenacanthus, such as Ot. distans, McCoy, and 0. gracillimus, Nob., is 

 very marked and is suggestive of closer relationship than has been assigned 

 them. These species of Ctenacanthus have been associated with the great 

 hybodoid spines, Ct. major, Agassiz, G. hyhodoides, Egerton, etc., simply on 

 account of their sharing with them the inconstant and unequally exhibted 

 character of the tuberculation or pectination of the longitudinal costae. As we 

 have before remarked, this is almost too variable and superficial a character to 

 serve as a band of generic union between organs of which the facies are so 

 diverse. We would, therefore, suggest to those who, hereafter in the possession 

 of more ample material, may be better able to adjust the classification of these 

 fossil fishes, the question whether the long, slender and flattened species of 



Ctenacanthus, cited above, should not be united with Leptacanthus junceus, L. 

 Jenkinsoni, and the. present species, in a generic group, distinct from both 



Ctenacanthus and Leptacanthus. 

 Formation and locality: St. Louis limestone, St. Louis, Missouri. 



Genus ORACANTHUS, N. and W. 

 Or acanthus pnigeus, N. and W. 



PI. XII, Fig. 3. 



Spine conical, short and robust, as broad at the base as high, 

 anterior margin nearly straight, posterior outline much curved, 

 anterior surface covered with relatively large stellated tuber- 

 cles, irregularly scattered toward the base, on the upper half 

 arranged in short oblique lines, extending from the anterior 

 border to the middle; posterior surface occupied by smaller 

 tubercles, without regular arrangement. 



