﻿ICHTHY0D0RUL1TES. 105 



The so-called Ctenacanthns? faUacn, J. Leidy, MS. (figured in the 

 Trans. Amer. Phil. Soc. vol. xi. 1857, pi. v. fig. 30), from the 

 American Carboniferous Limestone, is founded upon an indetermin- 

 able fossil in the Museum of the Academy of Sciences, Philadelphia. 



Spines differing only from Ctenacanthus in minor points have 

 been named as follows : — 



Anaclitacanthus, St. John & Worthen (Pal. Illinois, vol. vi. 1875, 

 p. 442), with the single species, A. semicostatus, St. John & Worthen, 

 ibid. p. 443, pi. xvi. fig. 14. — Upper Burlington Limestone ; Iowa. 



Eunemacanthus, St. John & Worthen (ojo. cit. vol. vii. 1883, 

 p. 246), with the single species, E. costatus, St. John & Worthen, 

 ibid. p. 246, pi. xxiii. fig. 2, previously named Ctenacanthus? cos- 

 tatus, Newberry & Worthen, Pal. Illinois, vol. ii. 1866, p. 120, 

 pi. xii. fig. 5. — St. Louis Limestone; Illinois and Missouri. 



Genus HOMACANTHUS, Agassiz. 



[Poiss. Foss. Yieux Gres Eouge, 1845, p. 113.] 



Dorsal fin-spines of small size, slender, more or less arched, much 

 laterally compressed, and gradually tapering distally ; sides of ex- 

 serted portion ornamented with few, large, smooth, widely-spaced 

 longitudinal ridges ; a similar ridge also forming a large anterior 

 keel; posterior face with a double series of large, downwardly- 

 curved denticles. * 



Homacanthus arcuatus, Agassiz. 

 ^ 1844. Hi/bodies gracilis, E. von Eichwald, Bull. Soc. Imp. Nat. Moscou, 

 vol. xvii. p. 827. 

 1845. Homacanthus arcuatus, L. Agassiz, op. cit. p. 113, pi. xxxiii. 



figs. 1-3. 

 1860. Homacanthus gracilis, E. von Eichwald, Leth. Rossica, vol. i. 

 p. 1600, pi. lv. fig. 9. 



The type species. 



Form. Sf Log. Devonian ; N.W. Russia. 



P. 2253. Fragment of spine. Egerton Coll. 



Homacanthus microdus, M'Coy. 



1848. Homacanthus microdus, F. M'Coy, Ann. Mag. Nat. Hist. [2] 



vol. ii. p. 115. 

 1855. Homacanthus ?nicrodus, F. M'Coy, Brit. Palseoz. Foss. p. 633, 



pi. iii. k. fig. 19. 



