WELLBURX : ON THE GENUS CCELACANTHUS. 
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the middle line. The lobe of this fin is always (as far as known) 
represented by a blank space, the baseosts having been destitute 
of, or very slightly ossified. The dermal rays are similar in character 
to those of the pectoral fin. 
Unpaired Fins. 
With the single exception of the first dorsal, the fins are lobate, 
the lobe being, however, more acute than that of the paired fins. 
First Dorsal Fin. — This fin shows no lobation as its dermal rays 
are opposed (as is well shown in a specimen in the author's collection) by 
their proximal ends, to the upper surface of a stout, well-ossified 
axonost (Ax. 1), whose upper end is somewhat expanded, whilst its 
lower is forked. The dermal rays are more robust and fewer in 
number than those of the other fins, but otherwise they show similar 
characters. 
Second Dorsal Fin. — This fin, as well as the anal, has a forked 
axonost (Ax. 2), which is, however, less robust than that of the first 
dorsal, and each fin is (as mentioned above) somewhat acutely lobate, 
the lobe showing as a blank space in the fossil state, the baseosts 
having been unossified, or very slightly so. The dermal rays of both 
fins are similar in characters to those of the paired fins. In position 
the first dorsal fin is opposite to the space between the pectoral and 
ventral fin, the second dorsal opposite to the space between the ventral 
and anal fins ; the latter fin arises close to the caudal. 
Caudal Fin. — This fin is always a conspicious feature of these 
fishes ; it is composed of a strongly-developed, symmetrical, principal 
fin (C F), and a small, feebly-developed, supplemental one (S C F). 
The principal caudal is supported above and below by a series of 
long, slender interspinous bones (I.S.), which equal, and are directly 
opposed to, the blunt distal extremities of the neural and haemal 
spines of the axial skeleton. A single stout dermal ray is connected 
with the distal end of each of these elements by an overlapping 
articulation. The sparse dermal rays of the supplemental caudal fin 
appear to be in direct contact with the spines of the axial skeleton. 
Swim-Bladder. — In the abdominal region of these fishes the 
ossified air or swim-bladder (S.W.) is always a conspicious feature ; 
