104 PALEOZOIC FISHES OF NORTH AMERICA. 
Berea shale at Vanceburgh, Ky., and now in the museum at Frankfort; aiso 
the partial ossification of the cranium and jaws of Diplodus, as shown by the 
specimens obtained by Professor Cope from the Upper Carboniferous of 
Texas and by the writer from the cannel coal of Linton, Ohio. Again, it 
is shown by the ossification of the rays of the pectoral fins of Ctenacanthus 
Clarkii of the Cleveland shale, and in the ossification of the jaws of Mazodus 
Kepleri from the Berea shale, Berea. Though generally considered as sela- 
chians and having certainly strong affinities with living sharks, the bones of 
the cranium and the jaws of these fishes are better ossified than those of most 
Cretaceous and Tertiary sharks and than those of the present day ; while 
the vertebral centra, following the common and inscrutable law of progress 
visible among fishes, have become more and more ossified in later ages 
Since the above description was written I have received from Prof. 
William Kepler a magnificent specimen of this fish, which enables me to 
make the description somewhat more complete. This specimen consists of 
the halves of a flattened calcareous concretion, which includes the anterior 
half of the body, with the under side of the head and pectoral fins very sat- 
isfactorily shown. The muzzle is rounded, the mouth terminal, the head 
eight inches long by six inches wide; the eye capsules are elliptical in out- 
line, two inches in the longest diameter; back of the eye are rounded plates, 
obscurely defined, which look as though they represented the opercula of 
the Ganoids and Teleosts. The respiratory slits are faintly indicated, but 
cannot be numbered; the interval between the head and the pectoral fins is 
occupied by the remains of a fibrous integument of which the fibers were 
transverse; the pectoral fins are eight inches long by five inches wide at the 
base, are very clearly defined, are widely expanded and have a reach of 
twenty-two inches from tip to tip; the basal cartilages are but obscurely 
shown. They seem to have formed meta, mesa, and propterygia, but this 
cannot be-asserted without further proof. The structure of the fin was evi- 
dently simpler than that of sharks now living, but on the same plan. We 
see nothing of the axial arrangement called archipterygium by Gegenbauer, 
so common in the ancient Ganoids, and surviving in Ceratodus. 
Formation and locality: Cleveland shale; Brooklyn, Ohio. 
