628 GEOLOGY OF OHIO. 
For the discussion of the zoological position, and the details of struc- 
ture of these Corniferous fishes, the reader is referred to the chapters of 
Vols. I and II Paleontology, that treat of them. By reference to these 
chapters, it will be learned that many of these early fishes were of great 
size and in some respects, certainly, of.quite high organization. Those 
of the present day which they most nearly resemble are the ganoids, 
represented in North America by the pike and the sturgeon, and the 
sharks which are widely distributed in existing seas. 
The exact stratum in which they first appear cannot be pointed out, 
but it is certainly quite low in the Corniferous series. It is among the 
heavy courses that constitute the base of the system. The remains that 
are found at this lowest horizon are the cranial plates, often unitedin a 
symmetrical skull, of the great ganoid, Macropetalicthys Sullivants. This, 
then, is the lowest and oldest of the fishes of the Devonian rocks of Ohio. 
The type specimens were furnished by Joseph Sullivant, Esq., of Colum- 
bus, to whose watchful and discriminating inspection of the State quar- 
ries when they were most largely worked, science is under great obliga- 
tions. Quite a number of the most interesting fossils of the for mation 
were gathered by him at this time. The remains of this fish so far 
known, all came from one horizon. | 
The next fish remains that we meet in ascending the series are those 
of Onychodus sigmoides, the teeth of which are not uncommon fossils in 
the middle Corniferous of Franklin county. The remainsof this genus, 
perhaps of this species, also, are found throughout a considerable verti- 
cal range. They can be followed into the Huron shale, at least. 
There came a time in the history of the Corniferous sea when fishes 
of this genus constituted its most conspicuous and abundant inhabi- 
tants.. There was scarcely a square foot of the sea-floor for hundreds of 
square miles that did not contain a tooth or plate of jaw of some fish 
that had met its fate in the waters above. There were considerable 
areas that seem to have been the gathering grounds, perhaps the breeding 
stations, of these tribes of the sea. Here their remains are accumulated 
to the exclusion of almost everything else. A six inch layer is chiefly 
composed of these remains. It is the bone bed to which such frequent 
reference has been made. 
Recent explorations show that over large areas on the floor of existing 
seas, the teeth of sharks are of very frequent occurrence. The dredge 
cannot scrape this floor foreven a few minutes without bringing up one 
or more teeth, sometimes white and fresh, and sometimes hidden in 
mineral concretions. The deposits are growing very slowly in all such 
seas and the dredge very likely brings up in one haul the accumulations 
