8 
ICHTHVOTOMI. 
Pleuracanthns arcuatus, Newberry. 
1856. Plmracanthns arcuatus, J. S. Newberry, Proc. Acad. Nat. Sci. 
Philad. p. 100. 
1873. Orthacanthw arcuatm, J. S. Newberry, Rep. Geol. Surv. Ohio, 
vol. i. pt. ii. p. 332, pi. xl. %. 4. 
Type. Spine. 
Spine (so far as known) not more than 0'15 m. in length, slightly 
arched, rounded in section, but flattened posteriorly. Denticles 
small, but very robust, numerous, and closely arranged in series 
along each margin of the posterior flattened area. 
Form. hoc. Coal-Measures : Ohio, U.S..\. 
P. 1734. Impression of spine in shale ; Linton. Egerton Coll. 
P. 5443. A similar fossil ; Linton. Enniskillen Coll. 
Pleuracanthns cylindricus (Agassiz). 
1843. Orthacanthus eylindrinis, L. Agassiz, Poiss. Foss. vol. iii. pi. 45. 
figs. 7 -9. 
1873. Orthocanthus, T. P. Barkas, Coal Meas. Palsoont. p. 20, figs. 39-42. 
1875. Orthacanthus cylindricus, J. Ward, [Proc.] North Staffs, Nat. 
Field-Club, p. 217. 
(?) 1879. Phricacantkns biserialis, .1. W. Davis, Quart. Journ. Geol. Soc. 
vol. XXXV. p. 186, pi. X. figs. 10, 17. 
1880. Lophacanthus taylori, T. Stock, Aun. Mag. Nat. Hist. [5] vol. v. 
p. 217, woodc. 
1880. Pleuracanthns cylindricus, J. W. Davis, Quart. Journ. Geol. Soc. 
vol. xxxvi. p. 331, woodc. 
(?)1881. Anodontacanthus acutus, J. W. Davis, loc. cit. vol. xxxvii. 
p. 428, pi. xxii. fig, 10. 
1888. Pleuracanthns (^Orthacanthus') cylindricus, R. H. Traquair, Geol. 
Mag. [3] vol. V. p. 101. 
Type. Spine. 
Spine of adult fish attaining a maximum length of about 0‘5 m., 
straight, or slightly arched towards the apex, and cylindrical in 
section. Denticles robust, pointed, arranged in double series upon 
the posterior aspect. 
Form. 6f Loe. Coal-Measures : Scotch Coalfield ; Northumberland, 
Yorkshire, Lancashire, Staffordshire. 
P. 1735. Spine, 16 inches (0'4 m.) in length ; probably from Dal- 
keith, near Edinburgh. Egertm Coll. 
P. 3175. An equally largo specimen, more abraded ; Dalkeith. 
Enniskillen Coll. 
P. 3176. Abraded fragment of small spine ; Low-moor, Yorkshire. 
Enniskillen Coll, 
