354 On the Fossil Fishes of the Carboniferous Limestone Serves of Great Britain. 
apex of the spine ; basally, it forms a terminal opening as in the Pleuracanths. A 
well-defined carina of smooth ganoine extends along the anterior surface of the 
spine ; the sides are ornamented by a variable number of narrow, smooth, longitu- 
dinal ridges, which towards the base increase by bifurcation. The ridges are 
separated by wide flat spaces, along which extend a number of minute longitudinal 
strize, and in some of the spaces there is also a row of widely-separated, irregulav, 
smoothly-rounded prominent tubercles, generally restricted to the spaces on the 
anterior portion of the spine, and occasionally restricted to the space on each side 
the anterior ridge. The posterior surface is depressed or hollowed, slightly 
pustulate, with a well developed median ridge. The postero-lateral angles are 
acute, with a row on each of small acuminate denticles, the points of which are 
directed upwards. 
Paucity of specimens probably led Prof. M‘Coy to believe that the form with 
a single row of tubercles on each side the anterior carina was of sufficient import 
to render necessary the institution of a separate species. A large series of 
specimens, however, proves that this is not so, every variety of tuberculation may 
be traced, and seems to be merely accidental. Specimens are not uncommon in 
which the several spaces have rows of tubercles, which for this reason would be 
classed with Asteroptychius ornatus, and at the same time have seven or cight, 
and near the base almost double that number of ridges. All the characters of A. 
semornatus may be found combined indiscriminately with those of A. ornatus, and 
for this reason they are both here included in the latter, which has priority. 
Several species of Asteroptychius have been found in the limestone of Burlington, 
Keokuk, St. Louis, &c., in Illinois, America. 
Formation and locality: Mountain Limestone, Armagh. 
He coli. Karl of Enniskillen. 
Genus.—Compsacanthus, Newberry. 
Compsacanthus, Newberry, J. 8., ‘Geol, Survey, Ohio,” Vol. Ip jos BSill 
““Spines, of small size, gently curved backwards ; exposed portion smooth and 
polished ; section at all points circular; a single row of relatively large, remote, 
depressed hooks set along the posterior median line.”~—(Wewberry.) 
Compsacanthus carinatus, Davis. 
(Pl XUV IS fos 1105) 
Spine, slightly curved, posteriorly imperfect, basal and apical terminations wanting. 
_ Portion preserved is 4°3 inches in length, antero-posterior diameter °65 inch ati 
the part nearest the base and ‘4 inch at the opposite end, where the lateral diameter 
is ‘22 inch. In transverse section the spine is elliptical ; an internal cavity extends 
from the base upwards to a short distance from the apex, the basal opening is 
terminal and wide ; the walls of the spine at that portion are thin, and consequently 
somewhat crushed and fractured ; towards the apex the walls are much thicker, and 
