FEOM THE YORKSHIRE CANNEL COAL. 431 



each side, which constitute a part of the pectoral arch and support the pectoral fins (p). The 

 bones are nearly 2 inches in length : their anterior extremities extend towards the median 

 portion of the branchiostegal apparatus, and are separated about an inch from each other ; 

 extending in a semicircle, the posterior extremities, somewhat flattened, are attached to 

 the pectoral fins. A process on the outer margin of the bones gave attachment to other 

 members of the pectoral arch, some elements of which are probably represented by the 

 specimens on PI. XLVII. figs. 4, 5, and 8. A separate example of the bone described 

 above is represented by fig. 12 on the same Plate. 



The vertebral column is in no instance preserved, but a decided impression remains in 

 specimens showing its course through the body. The absence of bony vertebrae indicates 

 that they were entirely cartilaginous, and in consequence have not been preserved. 

 Neural spines extended from the vertebral column towards the dorsal aspect of the fish. 

 They are strong and closely set ; there are twelve in the space of one inch in that portion 

 of the body surmounted by the anterior dorsal fin ; they are 1 inch to lh inch in length, 

 being longest and most obliquely placed near the caudal extremity of the fish. The base 

 of the spine attached to the vertebral column was divided, so as to afford a passage through 

 which the spinal cord passed ; the bifurcation extends - 3 of an inch. The rays are 

 hollow, the enclosed tube occupies about two fifths of the diameter of the spine, and the 

 encircling bone is of a very fine close texture. 



Prof. Huxley, in the Memoirs of the Geological Survey, decade xii. pp. 1G and 18, 

 considers that the dorsal fins of 0. lepturus are supported by large interspinous bones. 

 Numerous specimens of the species now described have afforded no definite indication of 

 such an interspinous bone ; but rather seem to show a more close connexion between 

 the spinous processes and the rays of the fin by smaller interspinous hones. 



The whole of the ventral portion of the fish, from the insertion of the pectoral fius to 

 midway between the ventral and anal fins, is occupied by an ossified air-bladder, and it 

 is worthy of remark that the whole of this region appears devoid of ribs or haemal spines : 

 bones are occasionally found lying across this region, but they appear to have been 

 displaced and fallen there accidentally. Posteriorly, haemal processes, corresponding to 

 those on the neural aspect of the vertebras, extend to and support the anal fin and the 

 inferior lobes of the caudal fius. The spinous processes are longer in this region than 

 elsewhere, and appear to be directly connected with the rays of the tail without the inter- 

 vention of interspinous bones (PI. XLVIII. fig. 2). The connexion between the neural 

 or h?emal spines and the fin-rays is not very clearly defined ; but, so far as can be 

 ascertained, there is no special arrangement such as was pointed out by the late Prof. 

 Agassiz (' Poissons Poss.' vol. ii. p. 168). He describes the interspinous bones as ossicles 

 which, instead of being attached by ligaments to the spinous bones on each side, are 

 attached to the end of one of them, so as to form its direct continuation ; and the ray, 

 properly so called, is stated to be forked at its base, and embraces the interspinous ossicle 

 in a manner similar to that of the spinous processes embracing the vertebrae. The 

 specimen referred to above exhibits very clearly the attachment of the caudal rays to the 

 spinous (?) bones. The basal extremities of the rays in this species are bent a little to 

 one side, and thin out to a point. The distal extremity of each spinous bone, which is 



