FISHES OF THE CARBONIFEROUS SYSTEM. 135 
identical. But it will be noticed that the plan of structure is essentially the 
same in both forms; that is, they are weak as compared with the correspond- 
ing bones in Dinichthys, are alike in wanting teeth or cutting edges and in 
possessing a deep furrow on the upper side of the anterior end. We lack 
materials for making satisfactory comparisons with all the other portions of 
the bony structure, but it may be said that the crania are very much alike 
and the peculiar articulation with the supra-scapular plates are the same in 
both. These latter plates are also generally similar in both species, and the 
same may probably be said of the clavicles, though the material in hand is 
too imperfect for accurate comparison. 
The dorsomedian plate is present in one of the specimens 7. Clarkii, 
also a large plate represented by PI. III, Fig. 1, which must have served for 
the protection of the under side of the body or head. Nothing correspond- 
ing to either of these two last-mentioned plates has been found in connection 
with the remains of 7. Agassizii, but the missing parts will doubtless be dis- 
covered in the future. The suborbital plates of the two species represented 
on PI. III, Fig. 2, and Pl. IV, Fig. 4, are very similar though distinct, and both 
are very much like the corresponding plates in Dinichthys and Coccosteus. 
From these facts it will be seen that the resemblances outweigh the differ- 
ences, and that the probabilities are decidedly in favor of generic identity. 
By the purchase of Dr. Clark’s collection Columbia College has come 
into possession of all the specimens of Titanichthys Clarkii known, and they 
are now in the Museum of the School of Mines. 
ON THE STRUCTURE AND RELATIONS or DINICHTHYS. 
Since my papers on Dinichthys were published in the Paleontology of 
Ohio in 1875, a large amount of material has been collected, chiefly by Mr. 
Jay Terrell, of Oberlin, Ohio, which throws considerable additional light 
on the structure of the great Placoderm that bears the name of its discov- 
erer, D. Terrelli. Also a number of new species have been found, some of 
which present most interesting peculiarities. D. Gouldii, for example, had 
enormous eyes and the eyeball was surrounded by a series of sclerotic 
plates similar to those of Ichthyosaurus. D. intermedius is another peculiar 
species, in which the denticles of the mandibles and maxillaries so conspicu- 
