On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 355 
the internal orifice reduced in diameter. The base was probably short, partaking 
generally of the character of that of the Pleuracanths. The lateral surfaces are 
convex and covered uniformly with longitudinal striz. Anterior surface slightly 
curved longitudinally: it is produced along the median line so as to form a 
prominent keel, which extends the whole length of the spine ; on each side of the 
keel there is a deep and broad groove, connecting it with each lateral surface. 
Posterior surface armed with a single row of recurved, pointed denticles extending 
the whole length of surface preserved. The denticles are large, broad at the base, 
tapering rapidly to the point, curved towards the base of the spine. 
The genus Compsacanthus was instituted by Dr. Newberry to comprise spines 
easily distinguished from all others by having a single row of large hooks along 
the posterior median line. The specimen serving as the type for Dr. Newberry’s 
description was externally smooth and slender, and circular in section. In addition 
to Newberry’s species, two species have been described by the writer, from the 
cannel coal of the West Riding of Yorkshire (Quart. Jour. Geol. Soc.,” Feb., 1880, 
p. 62). One of the Yorkshire species is triangular in section the other much com- 
pressed laterally : they have in each case a single row of denticles along the 
posterior surface. In the latter respect all the species agree ; but in order that the 
genus Compsacanthus may embrace all the species so far described it will require 
some modification of the original description. It may be as well, however, for the 
present to allow it to remain unchanged ; there is the possibility that further dis- 
coveries and investigation may show the necessity of new genera for some of the 
forms of spines with only a single median row of denticles. The species described 
above rests on a unique example in the Enniskillen collection, which certainly 
differs very greatly from the type species of the genus, and it is with considerable 
hesitation that it has been included in the genus. 
Formation and locality: Mountain Limestone, Armagh. 
Ex coll. Kav] of Enniskillen. 
Genus.—Cosmacanthus, Agass. 
Cosmacanthus, Agassiz, “‘ Poiss. Foss. vieux grés rouge,” p. 120. 
“Small spines, feebly arched, or almost straight ; entire surface ornamented by 
tubercles disposed in regular, longitudinal series; the most distinct are near the 
anterior margin of the spine, becoming gradually feebler towards the posterior 
margin, where they tend to disappear.” 
Only one species was known to Professor Agassiz from the Old Red Sandstone 
of Elgin. It was named Cosmacanthus malcolmsoni. 
Cosmacanthus marginalis, Davis. 
(Wel, SIGMWIDE, saree, Bh) 
Spine, 2°7 inches in length, basal and apical extremity each imperfect, greatest 
diameter near base 35 of an inch, gradually tapers to -2 at the part preserved 
