ICHTH YOD OKULTTES. 
Ill 
The following species have also been described, but there are no 
examples in the Collection :•— 
Asteroptychius bellulus , St. John & Worthen, Pal. Illinois, vol. vi. 
(1875), p. 439, pi. xvi. fig. 7.—Coal-Measures; Illinois 
and Iowa. 
Aster optychius elegcins , J. S. Newberry, Palseoz. Pishes N. America 
(Mon. TJ.S. Geol. Surv. no. xvi. 1889), p. 176, pi. xxv. 
fig. 4.—Waverly Group (Lower Carboniferous); Michigan. 
[Columbia College, New York.] 
Aster optychius sancti-luclovici, St. John & Worthen, op. cit. vol. vi. 
p. 437, pi. xvi. figs. 3, 4.—St. Louis Limestone; Illinois 
and Missouri. 
Aster optychius triangularis, Newberry & Worthen, Pal. Illinois, 
vol. iv. (1870), p. 370, pi. ii. fig. 4.—Burlington Lime¬ 
stone ; Illinois. 
Pour doubtful, fragmentary spines are also named Aster optychius 
Iceokuk, St. John & Worthen (op. cit. vol. vi. p. 436, pi. xvi. fig. 2), 
from the Keokuk Limestone of Illinois ; A. tenellus, St. John & 
Worthen (op. cit . vol. vii. p. 248, pi. xxi. fig. 4), from the Upper 
Coal-Measures of Kansas; A A tenuis , St. John & Worthen (op. cit. 
vol. vi. p. 438, pi. xvi. figs. 5, 6), from the Chester Limestone of 
Illinois ; and A. vetustus , St. John & Worthen (op. cit. vol. vi. p. 435, 
pi. xvi. fig. 1), from the Kinderhook Limestone of Iowa. 
Genus COSMACANTHUS, Agassiz. 
[Poiss. Poss. Yieux Gres Kouge, 1845, p. 120.] 
Syn. Geisacanthus, St. John & W r orthen, Pal. Illinois, vol. vi. (1875), 
p. 440. 
Dorsal fin-spines of small size, slender, more or less laterally com* 
pressed and very slightly arched ; sides of exserted portion orna¬ 
mented with longitudinal series of ganoine-coated tubercles, and the 
anterior margin often keeled ; posterior face flat or concave, without 
lateral denticles, but sometimes with a median keel. 
The type species of this genus (C. malcolmsoni ) is regarded by 
Pander 1 as founded upon a fragment of Placoderm armour ; and if 
this re-determination prove correct, the Carboniferous Ichthyodoru- 
lites recorded below must be named Geisacanthus. 
1 C. H. Pander, Placoderm. devon. Syst. 1857, p. 18. 
