168 PALEOZOIC FISHES OF NORTH AMERICA. 
Formation and locality: Cleveland shale; banks of Rocky River, below 
Berea, Ohio. It was there discovered by Dr. William Clark, for whom the 
specific name is given. The unique specimen which formed the base of the 
above description is in the geological museum of Columbia College. 
CTENACANTHUS CoMPRESSUS, Newb. 
Plate XXIII, Figs. 4-4”. 
Ctenacanthus compressus, Newb.; Annals N. Y, Acad. Sci., vol. 1, 1878, p. 191. 
Spine six to ten inches long by one and a half inches wide; much com- 
pressed; strongly arched above; anterior margin smooth; posterior flat- 
tened, with a well-marked rounded ridge along the central line; upper half 
of posterior face thickly set with conical recurved teeth; exposed portion 
wholly covered with fine longitudinal ribs, which are highly ornamented by 
closely approximated transverse lines; pectination finest on middle and 
lower portion of sides. 
The flattened, highly compressed form of this spine will serve to dis- 
tinguish it at a glance from any other species of the genus. The ornamen- 
tation is crowded and exact, and the organ must have been in life decorative 
as well as useful. 
I have recently received from Dr. William Clark a nearly complete 
spine of this species, only the unornamented base being absent. It is about 
nine inches long, and must once have been two inches longer. It is much 
curved backward, but more uniformly than the spines of Ct. Clarkui, N. The 
ornamentation is very similar to that of that species, but the form is much 
more compressed. It is possible, however, that the two species may have 
been the anterior and posterior dorsal defenses of the same fish. 
Formation and locality: Cleveland shale; Sheftield, Lorain County, Ohio. 
Found by Mr. Jay Terrell. Type specimen in the cabinet of Columbia 
College. 
CTENACANTHUS CLARKH, Nn. sp. 
Plate XXVI, Figs. 2, 3. 
Spines six to eight inches long, about one inch broad at the base of the 
ornamented portion, and five-eighths of an inch in greatest thickness; poste- 
