146 PALEOZOIC FISHES OF NORTH AMERICA. 
These, I am inclined to believe, are pectoral spines or bony supports of the 
pectoral fins, different in form from those of Coccosteus, but similar to them 
in function. These bones are generally ten or twelve inches in length, sub- 
triangular in section, with one broad, flat, or gently arched surface, while on 
the other side is an obtuse central keel with sloping sides. The ends are 
irregularly sharpened as though buried in cartilage. A narrow zone of 
the broader surface is flattened and smooth and may have been exposed, 
while the margins, ends, and under side were plainly covered with integu- 
ment of some kind. 
Probably these bones formed the anterior margin of the pectoral fins, 
articulating with the shoulder girdle by a cartilaginous joint. Confirmation 
of this view is afforded by the fact that they are distinctly in pairs, and not 
more than one or two have been found with any group of Dinichthys bones. 
Outside and inside views of these bones are given on Pl. V. 
THE Eyes or DinIcHTHys. 
Plate VII, Figs. 2, 2°. 
Only one head of Dinichthys has been found in which the parts were 
substantially in their proper positions. This was obtained in 1867 by Mr. 
H. Hertzer from a calcareous concretion near the base of the Huron shale, 
at Delaware, Ohio. The entire head was present, but the occipital portion 
was considerably mutilated in removing the stone which enveloped it. The 
anterior extremity of the head showed a broad, flattened muzzle with the 
great premaxillary teeth in place; behind these the maxillaries, with their 
denticulate margins, and beneath all the two mandibles with their extremi- 
ties turned up, forming triangular teeth, which interlocked with the premax- 
illaries. One suborbital bone was in its proper position, and in the deep 
sinus of its anterior and upper side the place of the eye could be determined, 
but nothing was left of it. 
In subsequent years many heads of Dinichthys Terrelli in a better or 
worse state of preservation were discovered by Mr. Jay Terrell on the shore 
of Lake Erie. In some of these the cranium was nearly complete, but the 
associated plates, jaws, and teeth were either absent or scattered irregularly 
