On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 538 
Genus.—Phoderacanthus, Davis. 
Spine, very large size, strong, gently and gracefully arched, wide at the base, 
gradually tapering to an acute apex ; transverse section, more or less ova], com- 
pressed laterally towards the basal extremity, internal cavity wide, opening 
terminally ; posterior cavity or groove absent, no posterior denticles ; surface 
uniformly covered with large smooth tubercles arranged on longitudinal ridges 
and also to a greater or less extent forming lines across the spine. Osseous walls 
of the spine pierced by several cylindrical canals extending longitudinally parallel 
with the surface. Base not preserved. 
The magnificent specimen which forms the type of this genus, is perhaps the 
largest example of a fin-defence hitherto discovered. The imperfection of the 
base renders necessary an addition of at least several inches to its length, and there 
is thus indicated a truly formidable and terrible weapon of offence, nearly or quite 
three feet in length. 
The genus Antacanthus, Dewalque, in several respects appears to possess 
characters similar to those of the genus now described. They resemble each 
other in the arrangement of the tubercles on the surface and in the possession of 
large cylindrical canals in the mass of the bony structure of the spines, but there 
is a great divergence in the form of the transverse section of the spines of the two 
genera; in the absence of large denticular tubercles on either the convex or 
concave margin of this one; and above all in the character which gives the name 
to the genus Antacanthus. Prof. de Koninck considers that the direction of the 
line dividing the exposed from the embedded portions of that species, showing its 
oblique implantation in the body, the line of demarcation forming an obtuse angle 
with the convex surface of the spine, and an acute angle with the concave surface 
which is the opposite of the arrangement in such genera as Ctenacanthus or 
Gyracanthus, indicates that the convex margin was the posterior one, and the 
concave the anterior one. The genus now introduced does not appear to diverge 
from the ordinary types of plagiostomous fishes, though the basal extremity of the 
spine is wanting, the rows of tubercles, already described as extending across the 
spine, no doubt indicate the line of demarcation to a large extent, and this being 
so, it is evident, that the line would form an acute angle with the convex border, 
and an obtuse one with the concave in the ordinary way. 
With the genus Oracanthus, with which this specimen has been erroneously 
associated to the present time, it possesses little in common except its pustulate 
surface; and in the character of the pustulations a comparison of the two will 
prove that they are quite distinct. The long comparatively slender and graceful 
form of this gerus, its thick convex walls, and arched form, are altogether different 
from the thin compressed section of Oracanthus, with its great basal opening and 
rapidly converging antero-posterior margins. In the peculiar duplicate arrangement 
of the spines (?) of Oracanthus, there is a still greater divergence from anything 
analogous in the form of this genus. 
