MR. J. W. DATIS Otf CHONDROSTEUS ACIPENSEROIDES. 613 



length, extending diagonally towards the dorsal surface of the 

 body. The interspinous bones are more slender than the neura- 

 pophyses ; they are forked at the base, and may afford pro- 

 tection to a second canal. Sir Philip Egerton* cites the description 

 by Prof. Owen of the vertebrae in the existing Sturgeon as com- 

 posed of " two superimposed pieces on each side, the basal portion 

 bounding the neural canal, the apical portion the parallel canal, 

 filled by fibrous elastic ligament and adipose tissue ; above this is 

 the single cartilaginous neural spine "% Of the fossil examples 

 described by Sir Philip Egerton, it is stated that the neura- 

 pophyses appear to be composed of two elements, corresponding to 

 the basal and apical cartilages of the Sturgeon ; but whether they 

 embraced a second canal, running parallel with the spinal cord, 

 could not be ascertained. The divided base of the apical neura- 

 pophyses or spines of the specimen now described affords conclusive 

 evidence that a second canal did exist in the fossil Chondrosteus, as 

 in the recent Sturgeon. In addition to the two sets of basal and 

 apical neurapophyses, the dorsal fin is supported by an additional 

 double series of bones. Connected with the apical neurapophyses 

 there is a series of interneural spines, more or less pointed at their 

 lower extremity, exceeding an inch in length, and with their 

 upper extremities expanded so as to afford attachment to a second 

 range of interneurals, to which the rays of the dorsal fin are 

 attached. Between the expanded and rounded extremities of the 

 two rows of interneural spines there is a continuous space which 

 indicates a cartilaginous attachment of no small size and strength ; 

 its decay has left the two sets of bones separated by 0*3 of an inch. 

 The interspinous bones are strong, and would afford a firm base of 

 attachment for the rays of the large dorsal fin. 



The dorsal fin extends along the back 6*5 inches, and its longest 

 rays are fully 6*0 inches in length. It is composed of 66 rays, of 

 which the anterior 15 are short and more or less rudimentary • 

 they occupy 1*75 inch of the base of the fin. The first rays are 

 short, thick, and imbricating ; they gradually increase in length to 

 about an inch. All are simple. The succeeding rays are trans- 

 versely jointed, and increase rapidly in length to the seventh ; the 

 twenty-second from the anterior extremity of the fin is the longest, 

 the succeeding rays gradually diminish to the posterior extemity of 

 the fin. All the rays, except the anterior fifteen, are jointed quite 

 from the base. The longest anterior rays bifurcate three inches 

 from the base, and the division is repeated nearer the distal extre- 

 mity. The bifurcation commences in the posterior rays nearer the 

 base in proportion to the length. 



The ventral fin is much disturbed. The fin-rays are numerous, 

 many of the fragments are thick and strong, and indicate somewhat 

 large and powerful fins. There is no appearance of ordinary pubic 

 bones ; but the anterior origin of the fin is marked by a Y-shaped 

 bone 1*2 in length ; it apparently forms a single piece for 0*5 inch, 



* Op. tit. p. 879. 

 Q. J. G. S. No. 171. 



t Hunterian Lectures, 8vo, vol. ii. p. 53 (1846 



2t 



