336 J. W. DAVIS ON A BONE-BED IN THE LOWER COAL-MEASURES. 



8. Pleuracanthtts ljsvisslmtjs, Agass. 



Yery rare. One specimen very perfect, nearly 8 inches in length, 

 and five eighths broad at the base, gradually tapering to a blunt 

 point. A double row of denticles extends, on each side from the 

 point, five inches along the spine. 



9. Orthacanthus cylindrictjs, Agass. 



The specimens of this species are generally small, rarely exceeding 

 three or four inches in length. They are found rarely in the bone- 

 bed. 



10. DlPLODTJS GIBBOSFS, AgaSS. 



Teeth rare. They are probably the teeth of Pleur acanthus or 

 Orthacanthus. Sir P. Grey Egerton has established their connexion 

 with the former ; and Dr. Newberry has found the spines of the latter 

 associated with the teeth of Diplodus in such a manner as to leave no 

 doubt that they belonged to the same fish. Both spines were 

 cephalic and nearly related. It is probable that different species of 

 Diplodus belong to each of these genera. 



11. Gen. nov. 



A spine hitherto undescribed. It is 4| inches in length, with a 

 diameter of -i- of an inch. The only specimen I have is crushed from 

 the base for 2 inches towards the apex ; the remaining portion is round, 

 without any hollow for the insertion of fin-rays, and gradually tapers 

 to a point. It is slightly curved, principally on the convex or pos- 

 terior portion of the spine. The surface presents a fibrous appear- 

 ance ; otherwise it is quite plain and smooth. On the concave surface 

 of the spine are eight denticles, separated from each other by about \ 

 of an inch, the intervals between those nearer the base being wider and 

 gradually becoming smaller nearer the point. The denticles are com- 

 paratively large, flattened, and blunt, and extend from the spine 

 nearly g of an inch. A second specimen, in the cabinet 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. A 

 transverse section, cut from the spine about one third its length 

 from the base and magnified twenty diameters, shows the internal 

 part to be rather more than half the diameter of the spine, and ap- 

 parently hollow. The bony structure surrounding the central part 

 is composed of numerous ridges without definite arrangement, be- 

 tween and amongst which are pits or vacuoles, the whole presenting 

 a labyrinthoid appearance. The bony part of the section has been 

 cracked both from the external and internal margins. The cracks 

 are filled up with iron pyrites. 



It is probably a cephalic spine allied to Pleur acanthus. 



12. Hoplonchtts, gen. nov. 



Three or four pines found in the bone-bed present characters 

 differing from any previously described. They are 1| inch long 

 and -j^- broad at the base. They are straight except a slight curve 



