52 PALEOZOIC FISHES OF NORTH AMERICA. 
in other portions set with scattered, somewhat remote, tubercles. The keel 
of the under side is buried in the rock, and its form cannot be made out; 
but one character is noticeable in which this differs from the dorsal shields 
of other species of Dinichthys ; that is, the keel did not extend to the posterior 
border, and that border projected from its base in a flange five-eighths of 
an inch in width. 
Unfortunately the specimen obtained by Mr. Gilbert remains unique, 
and little can therefore be said of the structure of the fish which it repre- 
sents. It is, however, certain that this was the dorsal shield of a Placoderm 
belonging to the Dinichthidze and probably to the genus Dinichthys, as no 
other is known to have had a dorsal shield of similar character. If so, it is 
interesting as being the oldest member of the genus of which we have any 
record. 
CoccostEUS OoccIDENTALIS, Newb. 
Plate XXV, Figs. 2, 2°. 
In volume 2, Pileeontology of Ohio, page 32, pl. 53, figs. 2, 2°, I have 
described and represented the dorsomedian and ventromedian plates of a 
small Placoderm which I have suspected to be a species of Coccosteus. A com- 
parison of these specimens with the corresponding parts of the dermal 
defenses of Coccosteus decipiens Ag. and C. cuspidatus Ag. shows so strong a 
resemblance that the conclusion that they are generically identical seems 
fully warranted. As I have elsewhere stated, it also seems highly probable 
that the little mandible which I described’ with the name Liognathus spatu- 
latus was a jaw of the same fish. To this conclusion I have been led by an 
examination of the jaws of Coccosteus in the British Museum, some of which 
have been recently found, and are much more complete than those figured 
by Pander and Agassiz. 
As the specimens referred to above remain up to the present time the 
only traces yet discovered of the existence of Coccosteus in America, more 
than usual interest attaches to them, and I have thought best to reproduce 
in this memoir the figures before published. 
The Corniferous limestone has proved to be a great treasury of ichthyic 
remains, and there is little doubt that future collectors will find in it not 
1 Paleontology of Ohio, vol. 1, p. 306. 
