370 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 10, 



the general contour of the body, remmding one somewhat of the head 

 of a Tortoise exserted below a high-backed carapace. In form it is 

 not unlike the head of a Leuciscus of the present day. The mouth 

 is small, and to all appearance edentulous, but of this fact there is 

 not sufficient evidence, from the imperfect condition of this part of 

 the specimen. The orbit is proportionately large. The preopercu- 

 lum is broad, of a semilunar outline and rough exterior. The oper- 

 culum and suboperculum are comparatively small. 



The junction of the head and neck describes an obtuse angle, from 

 which point the back rises abruptly for more than an inch, and then 

 slopes backwards and downwards to the base of the tail. The ventral 

 line forms a gentle curve from the lower jaw to the tail. No parts 

 of the internal skeleton are preserved. 



The pectoral fins are deficient. The ventral fins are indistinct, 

 but their position is clearly shown, exactly at the middle distance be- 

 tween the nose and the tail. 



The first dorsal fin is rather mutilated. It contains six or seven 

 rays, of which the fourth is the longest, the anterior ones being of 

 graduated lengths. The second dorsal fin is composed of at least 

 twenty rays, the sixth being the longest. The anterior rays or spines 

 of both fins are composed of a hard lustrous ganoine, similar to the 

 outer layer of the scales, and are sharpened at the points. The suc- 

 ceeding rays are flattened laterally, and are coated with similar 

 ganoine ; they appear consequently outwardly to be single and entire, 

 but on close inspection traces of the transverse articulations are 

 visible beneath the superficial layer. Their extremities appear to have 

 been dichotomous, but, in consequence of their more delicate and 

 perishable structure, the only remaining trace of these parts is a 

 stain on the matrix in which they reposed. The base only of the 

 anal fin remains. It contains about eight rays, of similar structure 

 and arrangement to those of the dorsal fin. It is situated nearer 

 the tail than to the ventral fins. 



The caudal fin is forked, and is composed of two very distinct 

 lobes, connected by a few distant rays, forming the centre of this 

 organ. The upper lobe consists of twelve rays, with frequent trans- 

 verse articulations and fimbriated extremities. They converge at the 

 base, and appear to have been supported by a process or processes 

 given off from the upper surface of the vertebral column. In the 

 lower lobe I comit eleven similar rays, apparently similarly divergent 

 from the under surface of the column. The central portion of the 

 fin is filled up by five or six weak rays, which subdivide at a short 

 distance from their bases. The scales project slightly over each lobe 

 of the tail, the extreme ones being in the centre of the upper lobe, 

 and not on the upper margin, as in a true heterocerque tail. 



The dermal investment is of great strength and soHdity. The 

 scales are numerous, and provided with a thick coat of ganoine. They 

 are also firmly interlocked and strengthened by an unusually large 

 overlap. The exposed parts, in consequence of the latter provision, 

 are high and narrow, except in the vicinity of the tail, where they 

 are more lozenge-shaped. The surface of the enamel is very uneven, 



