2 



BRITISH FOSSILS. 



ventral lines forming graceful and symmetrical curves. The pedicle 

 of the tail is shghtly prolonged and gradually contracted, but not to 

 so great an extent as in Fachycormus. The length of the body from 

 the nape to the base of the upper caudal lobe measures one foot ; 

 the greatest depth in front of the dorsal fin is four inches and three 

 quarters ; the pedicle of the tail two inches ; from the nape to the 

 dorsal fin is five inches, and thence to the tail seven inches. From 

 the pectoral to the ventral fins is three inches and a quarter ; from 

 thence to the anal fin, three inches and a half, and thence to the 

 lower caudal lobe four inches. The pectoral fin is composed of about 

 twenty -five rays, the first of which is much stronger than those 

 behind it. The ventral fins are much dislocated ; the number of the 

 constituent rays cannot therefore be ascertained. They appear to 

 have been broad, and the rays were thick, flattened, and frequently 

 subdivided transversely. The dorsal fin had a few slight fulcral 

 scales at its base, but neither in this or the other fins is there any 

 evidence of the first ray having a fringed margin. It contained not 

 less than fifty rays, closely arranged, flattened, and composed of very 

 numerous ossicles. The longest, forming the apex of the fin, measure 

 two inches and a quarter in length ; from the apex to the hinder 

 margin of the fin the rays decrease rapidly in length, forming with 

 the base line and anterior outline of the fin a nearly equilateral 

 triangle. The rays of the anal fin are too numerous and indistinct 

 to be accurately numbered. They correspond in character v/ith the 

 dorsal rays, but are shorter, and decrease in length more gradually 

 towards the tail. The base of the fin measures two inches and 

 three quarters, and it may be computed to have contained at least 

 seventy rays. The caudal fin is broader and not so deeply cleft as 

 that of Oxygnathus, but it corresponds with it in having the upper 

 lobe invested with scales. So strongly marked is this character 

 in both genera, that the doubts I have already expressed in the 

 description of Oxygnathus as to the propriety of considering that 

 a homocerque form, are much strengthened by the examination 

 of Cosmolepis. The rays composing the caudal fin of Cosmolepis 

 are far more numerous and frequently jointed than those of the 

 corresponding organ of Oxygnathus. Those of the upper lobe 

 decrease in length and substance as they approach the extremity, 

 and are supported by the prolonged upper limb of the organ, features 

 quite at variance with homocercal structure. There is no evidence 

 in this genus of the prolongation of the vertebral column into the 

 upper limb of the tail; on the contrary, there are symptoms of 

 the abrupt termination of the ossified vertebrae at the fork; it 



