140 PALEOZOIC FISHES OF NORTH AMERICA. 
To proceed with our analysis of the cranial plates of Dinichthys, we 
find the nasal plate just referred to succeeded behind by an oblong or 
elliptical plate, which corresponds to the posterior ethmoidal of Traquair in 
the figure cited. By Huxley it is denominated the ethmoid. In all our 
specimens of Dinichthys we find in this plate what is not indicated or 
described by Pander or Traquair, a remarkable conical opening, which I 
have considered the pineal fontanelle, so marked a character in the crania 
of the buckler-headed Siluroids, Avius, Phractocephalus, ete. It is broad- 
trumpet-shaped, though oblique below, and penetrates the exterior wall of 
the cranium by a minute but persistent circular orifice. 
The anterior angle of the head is formed by a quadrate plate, of 
which the outer margin is thin and excavated in an arch that forms the 
upper border of the eye-orbit. This is the plate called prefrontal by 
Huxley, preorbital by Traquair. It is followed behind by an oblong 
plate, very thick and massive, with a strong ridge below, bearing a robust 
columnar process, seen in both the views now given of the interior of the 
cranium of Dinichthys. The outer surface of this plate is marked in Dinich- 
thys as in Coccosteus by an intersection of the incised lines which constitute 
the surface ornamentation so conspicuous in both.) By Dr. Traquair this 
is called the post-orbital plate. Behind this is a triangular plate or bone 
which terminates in a point and is the prominent lateral angle of the head; 
more pointed and posterior than in Coccosteus. Dr. Traquair calls its homo- 
logue in Coccosteus the marginal plate. I have represented a small specimen 
of this bone from the head of D. Terrelli on Pl. L, Fig. 1. 
The middle portion of the posterior margin of the head in Dinichthys 
is formed by an extremely massive bone sometimes two inches in thickness, « 
which has a triangular point at its center behind, as in Coccosteus. This 
plate is rarely found detached in D. Terrelli, but one such, seen from below 
is shown on pl. 59 of volume 2, Paleeontology of Ohio. Near its center are 
the two pits, which are characteristic features of this bone in Homosteus, 
Heterosteus, and Titanichthys. By Owen and Huxley the plate occupying 
this position is called the supraoccipital; by Dr. Traquair, the medianoc- 
'The “lateral line system” of Traquair; the ‘‘ Haut (Schleim) Caniile” (mucus furrows) of von 
Koenen. 
