336 On the Fossil Hishes of the Carboniferous Limestone Series of Great Britain. 
the surface striz are large and broad, and in some instances, almost smooth. The 
base is divided irom the exposed portion of the spine by an oblique line, and 
occupies about one-fourth of the entire length of the spine. An open cavity extends 
from the base towards the superior extremity of the spine. It is not so deep as in 
the majority of the species of Ctenacanthus, but it remains open to a higher point 
than in any other species, and only the uppermost fourth of the spine ‘is enclosed. 
A transverse section exposes a small cavity im proportion to the thickness of the 
spine ; towards the base the anterior wall of the spine is very thick ; higher in the 
spine, the internal canal presents the form of a much compressed oval, but still 
nearer the apex the section is less compressed. 
The specimen described by M. de Koninck trom the neighbourhood of Felay, in 
Belgium, appears to differ from the Bristol specimens in the longitudinal strize 
being broader and less numerous, and in the possession of posterior denticles of 
which there is no evidence in the Bristol type. 
Formation and locality : Mountain Limestone, Bristol. 
He coll, Karl of Enniskillen. 
Ctenacanthus heterogyrus, Agass., MS, 
(JEG 2CILIOW., fiers, i, B 8.) 
Ctenacanthus heterogyrus—L. Agassiz, 1837. “Rech. Poiss. Foss.,” Vol. 1II., p. 177 (ind). 
3 * Portlock, J. E., 1848. “Rep. Geol. Survey, Fermanagh, é&c.,” p. 461. 
3 35 Giebel, C. G., 1842. “Wauna der Vorwelt,” Vol. I., pt. 3, p. 309. 
55 - Bronn, H. G., 1848. “Nomencl. Palxont.,” p. 355. 
‘s 5 m 1849. ‘Enumerator Paleont.,” p. 649. 
5 5 Morris, J., 1854. “Cat. Brit. Foss.,” p. 325. 
. +3 Pictet, F. J., 1854. “'Traité de Paléont.,” Vol. II., p. 290. 
5 5} Moy, F., 1855. ‘Brit. Paleoz. Foss.,” p. 625, pl. 31, fig. 32. 
, Morris and Roberts, 1862. “Quart. Jour. Geol. Soc.,” Vol. XVIII., p. 100. 
. 53 Bigsby, J. J., 1878. “Thesaurus Devon.-Carb.,” p. 351. 
3 . De Koninck, L. G., 1878. ‘* Faune Cale. Carb. de la Belgique,” p. 66, pl. vii., 
fig. 3. 
This speeres, named by Prof. Agassiz, but not described, was described by Prof. 
M‘Coy in the following terms:—“ Very short, rapidly tapering ; length of exposed 
portion three inches, at which length it forms an obtuse point, from a width at base 
of ‘5 inch (measured at right angles to the length), very slightly arched, the 
posterior outline nearly straight, the anterior one convex. Sides flattened, 
converging to the narrow anterior face, which is occupied by a flattened smooth 
ridge about twice as wide as those of the sides; lateral ridges extremely irre- 
gular in size, shape and marking; rather thick, separated by deep sulci less than 
half their width; ridges averaging four in two lines, at four lines in diameter, 
some of them thinning out above at irregular distances, other pairs uniting branch- 
wise Into one above, some appearing to taper to both ends; most of the ridges are 
nearly smooth in a great part of their course, or showing a more or less distinct 
crenulation on their sides (about three in the space of one line), from small opposite 
