On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 363 
Genus.—Gnathacanthus, Davis. 
Spine, triangular in section, long, and tapering. Lateral surfaces compressed 
with five or six longitudinal ridges, sometimes with intermediate rows of smooth, 
enameled tubercles. Anterior margin formed by the conjunction of the two lateral 
surfaces, forming an acute angle, armed with widely spaced denticles one-third the 
diameter of the spine in length, apex of denticles sculptured. Between the larger 
denticles are several smaller ones possessing similar characters. Posterior surfaces 
concave, wide, smooth or finely punctate with a slight median ridge. Postero- 
lateral angles sharp and well-defined, minutely and closely tuberculated. Internal 
pulp cavity large, conforming roughly to the external configuration of the spine. 
This spine bears a somewhat close resemblance to those of the genus Gampsa- 
canthus, St. J. and W. (“Palzeon.of IIl.,” Vol. VI., p.471), and especially to the species 
G. typus of the same authors (op. cit. p. 472, pl. xxii, fig. 12). It differs mainly, 
and to all appearance essentially in the character of the posterior surface and the 
angular junction of the postero-lateral surfaces. In Gampsacanthus the posterior 
surface is occupied by large, laterally compressed, subtrenchant denticles, slightly 
curved downwards, widely spaced, and of nearly uniform size. The lateral surface of 
the spine curves gradually to the base of these denticles. In the Armagh specimens, 
on the contrary, the postero-lateral angles are sharp and form ridges along which 
there are minute tubercles, whilst the posterior surface is broad, concave and 
smooth, with a slight median ridge but no denticles. 
The only spine at all resembling this one from British strata hitherto described 
is the Dipriacanthus of M‘Coy (Brit. Palzeoz. Foss.,” p. 627, pl. 3, K., fig. 18), and 
it only approaches it in the possession of denticles along the anterior margin ; it is 
quite distinct in form and general outline. 
Gnathacanthus triangularis, Davis. 
(12, SG NVIDOL, ite, 71.) 
Spine, imperfect ; length preserved 1‘75inches, greatest breadth ‘35. inch. Boththe 
basal and apical extremities are wanting and it is an uncertain approximation that 
the spine may have been four and a half to five inches in length. In transverse 
section the spine is triangular, the base, formed by the posterior aspect being 
half the length of the two sides, and the apex or anterior portion forming an 
acute but somewhat rounded angle. The lateral surfaces are straight or slightly 
depressed ; they are divided into six or seven rows of raised, pustulate, enamel- 
coated tubercles, circular in form and extending longitudinally along the surface ; the 
tubercles appear to have been only superficially implanted, many of them having 
been removed, leaving a hollow space to mark their former position. Between each 
row of tubercles there is a small ridge extending parallel with them. Anterior 
