2 



BRITISH FOSSILS. 



a close resemblance to PholidopJiorus, and should the positions of 

 the fins in relation to the anterior parts correspond, the general 

 form of the fish would come very near that of one of the shorter and 

 deeper species of that genus. There is also an approximation in 

 the character and mechanism of the scales, and I am therefore 

 inclined to place the genus next to Pholidophorus, rather than after 

 Ophiopsis, as suggested by Professor Agassiz. The locomotive 

 organs differ essentially from both these genera. In advance of the 

 dorsal fin are five strong fulcral scales, and the first true fin ray 

 has a fringe of short spines along the anterior border. The true rays 

 are six or seven in number, curving backv/ard from their insertions. 

 They are stronger than the fin rays of Pholidophorus, and differ 

 also in having the transverse articulations more numerous, and 

 continued nearly to the base of the component rays. The distal 

 extremities are finely fimbriated. The ventral fin contains six 

 rays, more slender than those of the dorsal fin. "GSie anterior 

 one is similarly fringed. The anal fin is composed of twelve 

 rays at least, but they are inserted so closely together, that 

 the exact number cannot be ascertained. The anterjor ray is 

 bordered in unison with the corresponding member of .the dorsal 

 and ventral fins. The component rays are extremely slender and 

 delicately fimbriated in their distal parts. All the fifs, although 

 small with reference to the size of the fish, are comparatively larger 

 than the corresponding organs of Pholidophorus ; they differ also 

 materially in having bordered margins, and being transversely sub- 

 divided to a much greater extent. The caudal fin is deeply forked. 

 The upper lobe contains sixteen rays ; the lower one is composed of 

 a like number. Both upper and lower m.argins are fringed, and a 

 few strong fulcral scales occur at the base of each. The body scales 

 extend rather further on the upper lobe than on the lower. The 

 styles supporting the rays are short and slender, and of equal length 

 in each lobe ; in the tail of Pholidophorus , the styles of the upper 

 lobe are very considerably longer than those of the lower lobe. 

 The fin rays are stronger in the upper lobe than in the lower. The 

 transverse articulations occur at shorter intervals than in the tail 

 rays of Pholidophorus ; in the lower lobe the divisions of the ossi- 

 cles are so nearly coincident that they form continuous elevated 

 lines sweeping across the fin, while in Pholidophorus and the 

 allied genera, the articulations of one ray generally impinge between 

 the articulations of the adjoining ray. The result of this arrange- 

 ment, combined with the frequency of the sub-divisions of the rays 

 of this and the other fins, would be to afford a greater amount of 



