ICHTHY0-D0EUL1TES. 
105 
The so-called Ctenaccinthus ? faTlacc , J. Leidv, 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 Ctenucanihus An minor points have 
been named as follows :— 
Anaditacanthus, 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 (op. cit. vol. vii. 1883, 
p. 246), with the single species, E . costatus, St. John & Worthen, 
ibid. p. 246, pi. xxiii. fig. 2, previously named Ctenaccinthus ? cos- 
tcitus, Newberry & Worthen, Pal. Illinois, vol. ii. 1866, p. 120, 
pi. xii. fig. 5.—St. Louis Limestone; Illinois and Missouri. 
Genus HOMACAMTHUSj Agassiz. 
[Poiss. Poss. Yieux Gres Bouge, 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 
heel; posterior face with a double series of large, downwardly- 
curved denticles. 
Homacanthus arcuatus, Agassiz. 
1844. Hybodus 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 specie^. 
Form. Zoc^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 microdus , F. M'Coy, Brit. Paheoz. Foss. p. 633, 
pi. iii, k. fig. 19. 
