334 On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 
Ctenacanthus major, Agass. 
(Pl. XLIL, figs. 1, 2.) 
Ctenacanthus major—L. Agassiz, 1837. ‘Rech. Poiss. Foss.,” Vol. III., p. 10, pl. iv. 
% 3 C. G. Giebel, 1848. “ Fauna der Vorwelt,” Vol. I., pt. 3, p. 308. 
ss 3 H. G. Brown, 1848. “Nomencl. Paleont.,” p. 355. 
%5 5 55 1849. “Enumerator Paleont.,” p. 649. 
5 3 F. J. Pictet, 1854. ‘Traité de Paléont.,” Vol. 1I., p. 290. 
PA ms J. Morris, 1854. “Catal. Brit. Foss.,” p. 323. 
4, ks Morris and Roberts, 1862. “ Quart. Journ. Geol. Soc.,” Vol. XVIIL., p. 100. 
> Young and Armstrong, 1871. “Trans. Geol. Soc., Glasgow,” Vol. ILI., Supplet. 
p. 70. 
z Z gee OS \ 1876. Catal. West. Scot. Foss.,” p. 61. 
A by J. J. Bigsby, 1878. ‘Thesaurus Devon.-Carb.,” p. 351. 
This spine is described by M. Agassiz as being elegantly arched in the form of a 
scythe. it attains a length of nearly two feet and is about three inches in diameter 
at the base. From the base it contracts insensibly towards the superior extremity, 
ending in a fine point. The surface is ornamented by a large number of small 
longitudinal ridges with intermediate rounded grooves. The ridges are divided by 
closely-imbricating obliquely transverse folds, which project over the groove on each 
side and form a denticulated margin. On the posterior surface of the spine, but 
only near the point, there extends a double row of small denticles. The latter are 
rounded, recurved towards the base, and pointed. The sides of the spine are com- 
pressed, but slightly rounded midway betwixt back and front. The transverse section 
is oval (Pl. XLIL., fig. 1a), rounded posteriorly, and somewhat sharply accuminate 
anteriorly. The line of demarcation between the exposed part of the spine and the 
smooth base which was embedded in the flesh, is very oblique. A deep and open 
cavity extends along the posterior face. It is prolonged in the form of an enclosed 
oval cavity almost to the apical extremity of the spine. 
If the size of the fish, to which these spines belonged, is proportionate to the size 
of living species which are possessed of dorsal spines, it must be admitted that it 
attained to gigantic proportions, and is, perhaps, the largest example of Ichthyo- 
dorulite occurring in the Paleozoic rocks of this country. Itis extremely probable 
that Ctenacanthus had two spines, one each before the anterior and posterior dorsal 
fins. Itis known that such was the case in Hybodus, as well as several other 
Selachoids which occur in a fossil state, and as found in the dog-fish existing on our 
own coasts at the present day. The spine represented on Pl. XLIL, fig. 2, was 
probably in front of the second one, (Pl. XLIL, figure 1), which is shghtly shorter, 
and broader and has a more robust character. 
The spines of this genus bear a marked resemblance to Céenacanthus maximus, 
described L. G. de Koninck (“ Faune du Caleaire Carbonifere de la Belgique,” Pt. I. 
