FISHES OF THE CARBONIFEROUS SYSTEM. 159 
so smooth, the edge so sharp and even, that it seems hardly possible that 
the plates could have been in contact with each other, but they were proba- 
bly set in the skin like the scutes of the sturgeons. 
None of these plates have yet been found quite entire, but some of 
them must have been eighteen inches in length by six inches in width; 
one end was acute, the other truncated, as though they had been set in rows 
touching and slightly overlapping at the ends. 
Genus DIPLOGNATHUS, Newb. 
Bones of cranium and body unknown; dentary bones long and slender, 
flattened, straight, spatulate behind, where originally covered with cartilage; 
anterior and exposed portions rising into points which diverge from the 
symphysis, giving a forked extremity to the lower jaw; conical, acute teeth 
formed from the jaw tissue are set along the outer margin of the mandibles 
and on the inside of the divergent extremities beyond the symphysis. A 
deep pit in each dentary bone marks the point of insertion of a powerful 
ligament, which bound the rami together and prevented splitting. 
The remarkable structure of the jaws on which the foregoing descrip- 
tion is based is, so far as known, without parallel in the animal kingdom. 
The dentary bones are produced forward into triangular, divergent points, 
of which the inner margins are set with sharp, recurved teeth. This formed 
a kind of forked rake, which must have been a very effective instrument for 
catching slender, slippery fishes or annelids, and was doubtless used for 
that purpose. 
One pair of mandibles and the anterior half of another are all the relics 
yet obtained of this fish. These are described and figured in this memoir. 
DIPLOGNATHUS MIRABILIS, Newb. 
Plate XI, Figs. 1-4; Plate XII, Figs. 1-3. 
Diplognathus mirabilis, N.; Annals N. Y. Acad. Sci., vol. 1, 1878, p. 188. 
Dentary bone attaining a length of eighteen inches by a width of two 
inches in the widest part; anterior half thickened as in Dinichthys, gently 
rising into an acute point anteriorly, which diverges from its fellow of the 
