FISHES OF THE CARBONIFEROUS SYSTEM. 169 
rior face excavated in a broad, shallow sulcus, which is bordered above by 
many acute, conical teeth; anterior margin subacute, nearly straight below, 
strongly curved above; sides gently arched, wholly covered with relatively 
fine and uniform, enameled, pectinated ridges, coarser toward the middle, 
where there are some twenty-five on each side, finer toward the base, where 
there are about forty on a side. The pectination of these ridges is every- 
where fine, but much closer near the base, where it forms a marked char- 
acter; margin of enameled surface at base curved upwards and backwards, 
reaching the posterior face about the middle; medullary cavity opening 
posteriorly up to the middle of the spine. 
In its general aspect this beautiful spine is not unlike Ctenacanthus 
speciosus, St. J. & W.,' but it is less broad and compressed, more acute and 
curved above, and the lateral ridges of the ornamented portion are much 
more closely pectinated. In size and general form it also resembles Ct. 
vetustus, N.,” but is thicker below, more acute, and curved above, and the 
longitudinal ridges are very much more numerous and more closely pecti- 
nated. ‘The ornamentation of the sides is more like that of Ct. compressus, N. 
(PL XXIII, Fig. 4), but it is much less compressed, and the transverse 
raised lines which form the pectination are closer. The posterior face is 
also without the central ridge which occurs in Cf. compressus and many other 
spines of Ctenacanthus. On the whole, this is one of the most exact and 
beautiful species of the genus, and I take pleasure in dedicating it to Dr. 
William Clark, who discovered it in the Cleveland shale near Berea, Ohio. 
Hopioncuus PARVULUS, Newb. 
Plate XXYV, Fig. 5. 
In the Paleontology of Ohio, volume 2, page 55, pl. 59, fig. 3, a small 
spine from the Cleveland shale is figured and described under the name of 
Ctenacanthus parvulus. In the notes on this fossil it is said : ‘This little spine 
is referred to Ctenacanthus with some doubt, as the longitudinal ribs show no 
tubercles or scales such as are usually found on the spines of this genus. 
It agrees with them, however, in the generalities of its form and markings, 
and scarcely affords material for the creation of a new genus.” 
1 Geol. Survey Illinois, vol. 6, p. 424, pl. 14, fig. 3. 2 Paleontology of Ohio, vol. 1, p. 326, pl. 35, fig. 3. 
