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f broad at the base, gradually tapering to a point. A double 
row of denticles extend on each side from the point, 5 inches 
along the spine. 
OrTH ACANTHUS CYLINDRICUS. Ag. 
The specimens of this genus are generally small, rarely 
exceeding 3 or 4 inches in length. They are rare in the Bone- 
bed. 
DirLODUS GIBBOSUS. Ag. 
These teeth are rather rare in the Bone-bed. It is probable 
that Diploius are the teeth of Pleuracanthus or Orthacanthus. 
Dr. Newberry, an American palaeontologist, has found the 
remains of the latter associated with the teeth of Diplodus in 
such a manner as to leave little doubt that they belonged to 
the same species. Both spines were cephalic, and nearly 
related. It is possible that the Diplodus teeth may belong to 
both genera. 
Gen : Is^ov. 
The spine is 4| inches in length, and has a diameter of 
of an inch. The only specimen I have is crushed from 
the base two inches towards the apex, tjie remaining portion 
is round, and gradually tapers to a point ; being slightly 
recurved, the surface presents a fibrous appearance, other- 
wise it is quite plain and smooth. On the concave por- 
tion of the spine are 8 denticles, each separated about a 
quarter of an inch. The intervals between those nearer the 
base being wider, and gradually becoming smaller nearer 
the point. The denticles are comparatively large and blunt, 
and extend from the spine nearly the ^ of an inch. A 
second specimen in the collection of W. P. Sladen, Esq., is 
completely separated from the matrix. It is nearly straight, 
and shows no evidence of a second row of denticles. It is 
probably a cephalic spine allied to Pleuracanthus. A trans- 
verse section cut from the sp. about ^ its length from the 
