FISHES OF THE DEVONIAN AGE. 13 
Up to the present time one nearly entire dorsomedian plate and a few 
fragments of others are all that we have obtained of this fish. When other 
portions of the plate armor shall be found they will probably be seen to 
correspond most nearly with those of Pterichthys. The tuberculation of the 
surface is, however, very different, and as the dermal ornamentation is char- 
acteristic in these old fishes, it is here undoubtedly indicative of differences 
which have generic value. 
ASPIDICHTHYS CLAVATUS, Newb. 
Plate XXXVIII, Figs. 3, 4. 
Aspidichthys clavatus, Newb.; Paleontology of Ohio, vol. 1, p. 323, pl. 35, figs. 1, 2. 
Of this large and remarkable fish very little is known, as only some 
portions of the dorsal plates have yet been found. These are, however, so 
peculiar and so different from anything else known to paleontologists, that 
they will serve to identify unmistakably one of the largest and most singu- 
lar of the great Placoderm fishes that inhabited the Devonian seas. 
The most significant fragment of Aspidichthys yet discovered is a nearly 
entire median dorsal plate obtained by Mr. Hertzer from the Huron shale 
at Delaware, Ohio. This plate is an elongated hexagon, or is of short 
coffin-shape, having, indeed, almost exactly the form of the dorsomedian 
plate of Pterichthys, but being a hundred times as large; for, while the 
largest plate of Pterichthys is twelve to eighteen lines, the corresponding 
plate of Aspidichthys is as many inches in each diameter, or, more exactly, 
is thirteen by seventeen inches, and a portion of it is wanting. It is more 
than an inch in thickness in the central portion, and is keeled below, as is 
the same plate in Dinichthys and Homosteus. The most striking feature in 
this plate is, however, its external ornamentation. This consists of knobs 
or bosses of smooth, shining enamel, of the size and form of split peas. 
In its general aspect this tuberculation resembles that of Pterichthys 
and Coccosteus, but differs strikingly in this, that the tubercles are perfectly 
smooth and polished, and show little of the stellate ornamentation which is 
to be seen on the plates of nearly all the great mailed fishes of the Old 
World. This character has doubtless generic value, but the form of the 
