FISHES OF THE CARBONIFEROUS SYSTEM. 155 
it as representing the species, to which I had given the name of D. curtus, 
but am rather inclined to the opinion that it is only a variety of D. intermedius. 
As mentioned in the general discussion of the relations of the genus, 
this plate corresponds so closely in form and markings with the so-called 
suborbital of Coccosteus that they must be homologous, and Dr. R. H. 'Tra- 
quair, in his paper on the relations of Homosteus and Coccosteus, in the Geo- 
logical Magazine for January, 1889, advances the view that they are really 
the maxillaries. Should that prove true, we shall be compelled to consider 
the dental plates with cutting edges (Pl. XLVII, Figs. 3, 4, 4") as modified 
teeth. 
On PL LI, Figs. 2, 3, I have given photographic views, half size, of 
the inside and outside of the anterior extremity of the cranium of D. inter- 
medius. 'These show distinetly the nasal plate, behind this the ethmoid, and 
on the sides the preorbitals. In Fig. 3 is represented the under side of the 
ethmoid with the pineal fontanelle, with the minute foramen which pierces the 
skull. On the left side of Fig. 3 is seen the roof of the eye orbit, and part 
of its upper margin complete. The suborbital plates in this specimen should 
be brought forward so as to form with the preorbital and postorbital plates 
a nearly circular orbit, which was about three inches in diameter. This 
indicates a large eye, yet not as large as that of D. Gouldii, although that 
was a smaller species. No traces of sclerotic plates have yet been found in 
connection with the head bones of D. intermedius, though this is not proof ° 
that they did not exist. Attached as they were to the eye, a movable and 
perishable organ, they would be very likely to be scattered, and if thin and 
delicate, destroyed. 
In this connection I would call attention, as I have elsewhere omitted 
to do, to the resemblance of the ring of sclerotic plates of Acanthodes to 
those of Dinichthys and Coccosteus. Dr. Ferd. Roemer has given a beautiful 
figure of the sclerotic plates of Acanthodes in the Zeitschrift der deutsch. 
geol. Gesellschaft, vol. 9 (1857), page 51, pl. 8, and he has shown that it 
consists of four pieces, as in Dinichthys Gouldii and Trachosteus Clarkii. In 
A. von Koenen’s figures of the sclerotic ring of Coccosteus’ it appears to be 
‘Beitrag zur Kenntniss der Placodermen, Abhandlungen der kéniglichen Gesellschaft der Wis- 
senschaften zu Géttingen, vol. 30 (1883), pl. 4, figs. 1, 2. 
