FISHES OF THE CARBONIFEROUS SYSTEM. 161 
these prove that it was allied to Dinichthys, and there is nothing improbable 
in the supposition that the jaws which belonged to this fish were similar to 
those I have described under the name of Diplognathus. In time this problem 
will doubtless be solved by the discovery of jaws associated with the armor 
of Glyptaspis or plate armor with Diplognathus. 
The mandibles of Trachosteus, so far as shown in the only specimens 
known, are strikingly similar to those of Diplognathus, and as in these speci- 
mens the anterior extremity is wanting, I at one time had a suspicion that 
it would be necessary to unite these two genera, but on comparing their 
mandibles it was found that there were marked differences, which proved 
that they could not be united. Hence we are compelled to say that the 
jaws of Diplognathus cannot be associated with the remains of any other fish 
found in the Cleveland shale unless it be Glyptaspis. 
Genus MYLOSTOMA, Newb. 
Dipterine Ganoids of large size, of which as yet only the dentition is 
certainly known; the teeth or dental plates consist of strong and massive 
tables of bony tissue, becoming more dense and enamel-like toward the 
triturating surface. They apparently formed several pairs on both the upper 
and lower jaws. The principal plates of the lower jaw had long-oval or 
spatulate crowns three to six inches in length by one to two inches wide 
and half an inch or more in thickness, supported by strong, vertical, spatu- 
late bones, which projected downward and backward, terminating posteriorly 
in thin, rounded margins. The upper surface of the crown is raised into a 
more or less prominent tubercle which is situated near the exterior margin 
and slightly anterior to the middle. Another pair of teeth apparently be- 
longing to the lower jaw are triangular in outline, with one straight and 
shorter side, where they join and an exterior arched and longer side. In the 
posterior end of each is a deep notch, apparently for the reception of the 
blunt-pointed anterior end of one of the larger dental plates described above. 
The surfaces of these triangular teeth are convex. Possibly other teeth 
were associated with these to form the pavement of the under jaw, but that 
is not yet demonstrated. 
MON xvI——11 
