FOSSIL FISHES. iit 
the anal nearly opposite the posterior dorsal. ‘The scales are ovoid in outline, 
relatively thin, imbricated, with one-third to one-half the surface exposed, 
and this ornamented with raised enamel lines. The bones of the head and 
pectoral arch are granulated, or ornamented with raised, tortuous, interloclk- 
ing, arid interrupted ridges. The air bladder was ossified, the vertebral 
column cartilaginous, and having disappeared in fossilization, its place is rep- 
“resented by a smooth band, which is continuous from the head to the ex- 
tremity of the tail. In the caudal and supplemental caudal fins the course 
of the spinal cord is marked by rows of scales of diminished size. The 
neural and hzemal spines were ossified, and are distinctly shown in the 
fossil state. The rays of the caudal fins were supported by interneural and 
interhzemal spines, to the extremities of which they are attached by sheathing 
splices. As in ail the other members of the family, the fin rays are hollow, 
and the sides are frequently crushed together in the fossil state, but in 
Diplurus the walls were strong and the rays generally retain their forms. 
As in Holophagus and some of the living siluroids (Doras, Plecostomus, ete.), 
the fin rays are coated with short, closely-set, acute spines. The dentition 
is yet unknown, not being shown in any of the specimens found up to the 
present time. Whether the teeth were flat and obtuse, like those of Undina, 
or acute, as in Cwlacanthus, remains to be determined by further observa- 
tion. 
Diplurus shows throughout its structure all the characteristic features 
of the remarkable family to which it belongs. Its resemblance to Cala- 
canthus, Holophagus, and Macropoma is so close, that if they all occurred 
in the same geologic formation we should hardly be justified, with our 
present knowledge, in regarding them as more widely separated than are 
different species of the same genus. This similarity among the members 
of the family has been noticed by Professor Huxley in his remarks on 
Celacanthus, Holophagus, Undina, ete.’ 
It is one of the most surprising and interesting facts in the history of 
fishes that this family should appear so suddenly, spread over the whole 
northern hemisphere, retain all the details of its highly specialized struct- 
ure through the Carboniferous and Mesozoic ages, and then disappear as 
. 
