338 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
Prof. Agassiz in his description of this spine says, “ I know as yet only one figure 
of this spine, which has been communicated to me by Dr. Buckland, and which I 
have had copied in the plate cited above. There is represented the inferior part of 
a large spine, very thick in proportion to its length, of which the exposed surface 
is covered with small transversely striated tubercles, disposed in longitudinal and 
parallel series. The base is smooth; the line of demarcation between the part 
embedded and that which was exposed is very oblique, and arched towards the 
anterior margin. The posterior basal cavity is very large and deep.” 
A perfect specimen in the cabinet of the Earl of Enniskillen is nine inches in 
length; the greatest breadth is 1°4 inches, at the junction of the exposed and 
basal portions. The posterior face is almost straight, except for a short length 
near the superior extremity, which is deeply curved. The anterior margin is 
eracefully arched from the apex to the base. The proportion of the spine which 
was embedded in the body of the fish is extremely large, and forms about two- 
thirds of the whole surface. The smooth base extends 4°5 inches along the anterior 
surface, from which it extends, with a very oblique curvature, to 1°5 inches from 
the point on the posterior surface. There is no appearance of posterior denticles. 
This species in some respects bears a close resemblance to Ctenacanthus 
spectabilis, St. John and Worthen, (“Geological Survey of Illinois,’ Vol. VI., 
p. 420, pl. vi, fig. 1). Inthe latter, however, the base is much smaller in proportion 
to the exposed part of the spine, and the angle dividing the two is not nearly so 
oblique as in C. brevis, Ag. The peculiar way in which the costz are deflected 
towards the posterior margin in the Kinderhook specimen, does not occur in the 
Armagh one, and the form of the tubercles set along the costze of the two species 
is quite distinct. 
Formation and locality : Mountain Limestone, Armagh, 
Ez coll. Karl of Enniskillen. 
Ctenacanthus denticulatus, M‘Coy. 
(Pl. XLIV., fig. 4.) 
Ctenacanthus denticulatus—F. M‘Coy, 1848. ‘Ann. and Mag. Nat. Hist.,” 2nd Ser., Vol. IT.,p, 116. 
J. F. Pictet, 1854. “ Traité de Paléont.,” Vol. II., p. 290. 
J. Morris, 1854. ‘Catal. Brit. Foss.,” p. 323. 
3 % F. M‘Coy, 1855. ‘Brit. Palzeoz. Foss.,” p. 625, pl. 3 K, fig. 16. 
J. J. Bigsby, 1878. ‘“Thesaur. Devon.-Carb.,” p. 351. 
‘Spine, nearly straight, slightly curved towards the apex ; length of naked 
portion 5°5 inches, length of the rapidly tapering base two inches, width near base, 
nine lines; section truncato-elliptical, sides slightly convex, front narrow, 
rounded ; posterior face wide, depressed, concave at both sides, with an obtuse ridge 
in the middle, the lateral angles closely set with a row of numerous, small, conical, 
downward-curved teeth on each, their own length apart; longitudinal ridges 
