FISHES OF THE CARBONIFEROUS SYSTEM. 139 
very peculiar and effective style of dentition. This plate I have called 
the maxillary, though distinctly stating that it was not proved to be the 
homologue of that organ in other fishes or the higher vertebrates. In D. 
Hertzeri, of the Huron shale, the first described species of the genus, the 
‘‘maxillaries,” like the margins of the mandibles, are set with acute denti- 
cles; and in D. intermedius, now described, we see a connecting link 
between the two forms, the posterior margins of the cutting edges of the 
maxillaries and mandibles being set with compressed and scarcely functional 
denticles. The relations which the plates I have called maxillaries sustain 
to the ‘“suborbital plates” of Owen, the ‘“maxillaries” of Traquair, are 
intimate, since the former rest upon and are supported by the processes of 
the latter, which pass beneath and form the lower margins of the eye-orbits. 
Yet there was no bony union between them, and they are always found 
separated. Hence, if the suborbital bone is to be regarded as the true 
maxillary, these cutting plates must be considered as modified teeth; a 
view which I am inclined to adopt. 
A similar question arises with reference to the homologies of the dental 
organs at the anterior extremity of the head. Professor Huxley calls the 
T-shaped plate which terminates the snout the pre-maxillary, while Dr. 
Traquair calls it the anterior ethmoid, and two little plates which are situ- 
ated on either side of it in Coccosteuws—plates not mentioned by Huxley— 
the pre-maxillaries. In Dinichthys there were apparently no plates corre- 
sponding to these so-called pre-maxillaries in Coccosteus, but instead are 
two great triangular dental organs, which meet on the median line and, 
diverging, interlock with the upturned points of the mandibles. These teeth 
I have provisionally called the pre-maxillaries, and if they were not such, 
the nasal plate must be considered as the pre-maxillary, and my ‘‘pre-max- 
illaries” as teeth, which are supported by the nasal bone in part and partly 
by the anterior edge of the preorbital plate. It will thus be seen that the 
dentition of Dinichthys, though remarkably effective, is very peculiar, and, 
so far as I know, without analogy with that of any other vertebrate than 
Protopterus ; with this it has much in common, especially if we consider the 
two great anterior teeth as the homologues of the two so-called vomerine 
teeth of Protopterus annectens. ‘ 
