ICHTHYODORULITES. 
139 
The following species of Oracanthus have also been described, 
but, in some cases, the distinctive features are very slight, and if 
such were regarded as of specific value in Britain, 0. milleri would 
be considerably subdivided :— 
Oracanthus armigerus , R. H. Traquair, Trans. Edinb. Geol. Soc. 
vol. v. (1887), p. 313 (name only), and Geol. Hag. [3] 
vol. v. (1888), p. 86.—Calciferous Sandstones; Abden, 
Eife, and Eskdale, Dumfries. Carboniferous Limestone ; 
Ayrshire. [Collection of R. Craig, Esq., and also portion 
of fish in Edinburgh Museum.] 
Oracanthus ? obliquus, St. John & Worthen, Pal. Illinois, vol. vi. 
(1875), p. 477, pi. sxii. fig. 16.—Upper Keokuk Lime¬ 
stone ; Illinois. 
Oracanthus rectus , St. John & Worthen, op. cit . vol. vii. (1883), 
p. 257, pi. xxv. fig. 3.—Chester Limestone ; Illinois. 
Oracanthus trigonalis ; Pnigeacanthus trigonalis , St. John & 
AVorthen, op. cit. vol. vii. p. 259, pi. xxiv. fig. 4.—St. 
Louis Limestone; Illinois. 
Oracanthus vetustus, J. Leidy, Proc. Acad. Nat. Sci. Philad. vol. vii. 
1856, p. 414, and Journ. Acad. Nat. Sci. Philad. [2] 
vol. iii. (1856), p. 161, pi. xvi. figs. 1-3 ; St. John & 
Morthen, op. cit. vol. vii. p. 255, pi. xxiv. fig. 2: Ora¬ 
canthus consimilis , St. John & Worthen, op. cit. vol. vi. 
p. 478, pi. xxii. fig. 15.—Uj)per St. Louis Limestone; 
Illinois, Missouri, and Iowa. [Academy of Natural Sci¬ 
ences, Philadelphia.] 
Closely related to Oracanthus is the very large spine described as 
follows: — 
Antacanthus insignis, G. Dewalque, Ann. Soc. Geol. Belg. vol. v. 
(1877), p. lx; L. G. de Koninck, Eaune Calc. Carb. Belg. 
pt. i. pp. 72, 73, pi. viii. figs. 1-3.—Lower Carboniferous 
Limestone ; Liege. [University of Liege.] 
Genus GITHAC.ABJ'X’K'U'Sj Agassiz. 
[Poiss. Loss. vol. iii. 1837, p. 17.] 
Syn. Mitrodus , R. Owen, Trans. Odontol. Soc. vol. v. 1867, p. 338. 
Spines of two distinct types, the one evidently connected with 
fins, the other free. Fin-spines elongated, robust, more or less 
arched, irregularly rounded or oval in transverse section, except 
towards the unworn apex, which is compressed; base of insertion 
large, with the internal cavity open for a considerable extent pos- 
