364 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
surface rounded and narrow, studded with denticles of two sizes, the larger are 
about 35 inch apart and extend ‘1 inch from the surface, inclining slightly towards 
the apex of the spine. The basal portion of the denticle is round and smooth ; 
The apex acuminate, with a series of minute ridges extending from the point down- 
wards. Between each of the large denticles there are three or four smaller ones, 
resembling the larger onesin miniature. Posterior surface slightly concave, fibrous, 
minutely and irregularly pitted, with a median ridge, small but well-defined. The 
postero-lateral angles are closely studded with minute enamel-tipped tubercies. 
The internal orifice is large, partaking generally of the external form of the spine. 
Whether it formed an external sulcus at the basal portion of the spine, or was 
enclosed with a terminal opening only, the spine is not well enough preserved to 
show. 
Formation and locality : Mountain Limestone, Armagh. 
Ez coll. Kari of Enniskillen. 
Gnathacanthus striatus, Davis. 
(PI. XLVIIL., fig. 12.) 
Spine, imperfect; base wanting, part preserved 1-6 inches in length, greatest 
breadth *3 inch, at basal extremity. Slightly curved posteriorly, gradually 
tapering towards the superior extremity which terminates acutely. Transverse 
section, triangular, the sides meeting at an acute angle to form the anterior margin, 
base shorter than sides, internal cavity large and oval. Lateral surfaces ornamented 
by aseries, six or eight, of longitudinal, enamelled, strong, inosculating ridges. The 
anterior margin is occupied by a row of closely-implanted compressed denticles, wide 
at their base, curved downwards, and sharply pointed. Each of the latero-posterior 
margins also possesses a line of denticles, smaller and finer than the anterior ones, also 
curved downwards and separated from each other by about double their own 
diameter. | 
The species differs from the previous one in its less decidedly triangular form and 
more especially in the ornamentation of its sides. The pustulate enamel-coated 
tubercles of G. triangularis are replaced by a much more decided series of ridges than 
occurs in that species. The anterior row of denticles and the general form of the 
spine, however, are sufficiently characteristic to renderits genuine position undoubted. 
Formation and locality : Mountain Limestone, Armagh. 
Hx coll, Kar] of Enniskillen. 
Genus.—Cladacanthus, Agassiz. MS. 
Cladacanthus—L, Agassiz, 1833. “Poissons Foss.,” Vol. III., p. 176. (MS.) 
Erismacanthus—M‘Coy, 1848. “Ann. Nat. Hist.,” 2nd ser., Vol. II., p. 119. 
‘Spine, of three divaricating portions; tirst, a large, compressed, finely striated base, 
which entered the flesh ; secondly, a short, strongly compressed, rapidly tapering 
