On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 343 
teeth. In the specimen from the Enniskillen collection the posterior margin is 
exposed and a row of recurved teeth is very clearly exhibited. Unfortunately the 
specimen forming the type of Agassiz is buried in a hard matrix and the posterior 
margin cannot be seen, but the two are so clearly related and possess so 
mary features in common than it is very probable, could the surface be exposed 
without too great risk to the specimen that it would be found to possess posterior 
denticles. After careful consideration it appears advisable to consider the specimen as 
belonging to the genus Ctenacanthus. 
The more rapidly contracting form of this species, the absence of an anterior 
median keel, and the peculiarities of the ridges, separate it specifically from Ctena- 
canthus levis. 
Formation and locality: Mountain Limestone, Armagh. 
Ex coll. Geological Society’s Museum. 
Ctenacanthus sulcatus, Agass. 
(Pl. XLV., fig. 3.) 
Ichthyodorulithes bristoliensis, Buck. and De la Béche (MS.) 
Onchus sulcatus—L. Agassiz, 1833. “Rech. Poiss. Foss.,” Vol. III., p. 8, pl. 1, fig. 6. 
a 3 C. G. Giebel, 1848. ‘Fauna der Vorwelt,” Vol. L., pt. 3, p. 302. 
a Ss H. G. Bronn, 1848. “ Nomencl. Palzont.,” p. 843. 
= as . 1849. ‘ Enumerator Paleont.,” p. 652. 
3 ee F. J. Pictet, 1854. “ Traité de Paleont.,” Vol. II., p. 284. 
35 $6 J. Morris, 1854. “Catal. Brit. Foss.,” p. 334. 
5 Bs Morris and Roberts, 1862. “ Quart. Jour. Geol. Soc.,” Vol. XViIL, p. 101. 
A 535 J. J. Bigsby, 1878. ‘Thesaurus Devon.-Carb.,” p. 359. 
Spine, more or less arched, medium size, perfect example five to six inches in 
length, breadth 1:0 inch, gradually tapering towards the point, base one-fourth the 
length of the spine, division between base and exposed part forms a slightly sig- 
moidal curvature: transverse section oval, much compressed laterally ; internal 
cavity situated near posterior surface, comparatively small and broad. ‘The lateral 
surfaces are ornamented by peculiar longitudinal ridges, which are described by 
Prof. Agassiz as being especially distinguished by the irregularity of their furrows 
and of the ribs which separate them, some of them being double the width of 
others ; they, however, have all a very flat surface. The anterior surface is formed 
by a broad ridge which is divided near the base into three branches, it is rounded 
and more thickly coated with enamel than the lateral ridges. The posterior cavity 
is large, and open at the basal extremity, a deep groove being continued on the ex- 
ternal surface towards the apex of the spine. It appears doubtful whether speci- 
mens of this species have been found which exhibit the latero-posterior angles 
with sufficient clearness to show the posterior denticles. Prof. Agassiz states that 
Dr. Buckland sent to him a drawing of a specimen, well preserved, from which it 
appeared that the spine had a double row of small denticles along the superior 
TRANS, ROY. DUB, SOC., N.S., VOL. I, 3L 
