Upper Devonian Placoderms of Ohio. — Claypole. 353 
side of the Appalachian gulf in New York and Pennsylvania 
are of totally different species. Few or none of either coast 
passed over the intervening depths to the opposite shore. The 
fauna of the New York Catskill and Chemung differs entirely 
in species from that of the Cleveland Black shale, though they 
were more or less closely contemporaneous. We are hence 
led to the inference that these great placoderms were shore- 
haunting or estuarine fishes, frequenting the mouths of rivers 
and the adjoining seas or possibly ascending the streams 
themselves like the mud-fishes of the present day. To such 
creatures the deep seas are barriers as impassable as the dry 
land. In the shore muds of the Appalachian gulf therefore — 
the black shales of the present day — their remains may natur- 
ally be sought and here it is that they are found. 
Below the barren Erie shales we find in central Ohio another 
black bed sometimes 300 feet in thickness and so closely 
resembling the Cleveland shale that the two can be distin- 
guished with difficulty, if at all. In the lower shale we come 
upon another fish fauna consisting of a few kinds more or 
less like those of the upper shale, but all specifically different. 
The following described by Dr. Newberry are all that we yet 
know : 
Dinichthys hertzeri Callognathus serratum 
Gonioclus hertzeri Onychodus ortoni 
Callognathus regulare Aspidichthys clavatus 
Here is a group of fishes, one of which is so closely allied to 
the larger genus in the Cleveland shale that it bears the same 
name, Dinichthys. The paleontologist sees in this a proof 
that the genus continued to exist all through the succeeding 
barren interval, but that either its relies have been destroyed 
or that these fish left the area for a time and returned to it 
later. Which of these explanations must be adopted in the 
present case we shall show below. 
There is an easy way of connecting these two faunas. I 
have said that the Erie shale thins away to nothing, thus 
letting one of these black shales down upon the other in the 
central and southern part of Ohio. Here then we can read 
an uninterrupted history and can trace the connection be- 
tween Dinichthys of the lower and Dinichthys of the upper 
Cleveland shales, and the ancestry of our Upper Devonian 
placoderms is found in their Middle Devonian predecessors. 
