FISHES OF THE CARBONIFEROUS SYSTEM. 143 
The mandibles of Dinichthys Terrelli and D. Hertzeri have been already 
fully figured and described.’ I now give good figures of the mandibles of 
D. intermedius and less satisfactory ones of more imperfect jaws of some of 
the smaller species.” They exhibit considerable diversity of form, and it is 
desirable that when more perfect specimens are found they shall be repre- 
sented so as to show the range of variation in this part of the bony structure. 
In D. Gouldii the cutting edge was nearly straight, the bevel more obtuse 
than in the larger species; the posterior end was also much narrower, 
straighter, and thicker relatively than in any other known to me. 
My remarks on the relations and structure of Dinichthys contained in 
the second volume of the Paleeontology of Ohio were written before we had 
obtained a complete suite of the bones, and I was therefore unable to point 
out all of the features which it had in common with Coccosteus. Later dis- 
coveries strengthen the force of the comparison then made. The cranial 
plates, the suborbitals, the suprascapular and dorsal plates are as much alike 
as possible with the differences in the general form of the head, which is hex- 
agénal in Coccosteus and triangular in Dinichthys. So the plastron is com- 
posed of homologous plates having practically the same number and similar 
forms, although in Coccosteus the sternal element consists of an anterior 
triangular plate and a rhomboidal central one, while in Dinichthys they are 
connected by a bony band. 
It has been supposed that the dentition of Coccosteus and that of Dinich- 
thys were radically different, but I have learned that they were very much 
alike. The mandibles of Coccosteus that have been figured are all imperfect, 
the anterior ends being crushed, distorted, or wanting; yet, as I have men- 
tioned elsewhere, I recently found in the South Kensington Museum a man- 
dible of Coccosteus which was a perfect miniature of that of Dinichthys, being 
spatulate posteriorly and having the anterior end turned up to form a con- 
‘spicuous denticle. In regard to the dentition of the upper jaw in Coccosteus 
we are as yet not well informed, and therefore a satisfactory comparison can 
not be made. 
The foramen which penetrates the center of the head of Dinichthys, 
passing through the middle of the ethmoid plate, has been referred to above. 
1 Paleontology of Ohio, vol. 1, p. 316, pl. 30; vol. 2, pp. 7,8, chart V.  * This Monograph, Pls. X, LXIII. 
