

FROM THE YORKSHIRE CANNEL COAL. 429 



in parallel rows from the dorsal to the ventral surface, diagonally, with a slight sigmoidal 

 curvature. The scales enveloping the lohes of the several fins differ from those of the 

 body only in size ; they are much smaller, decreasing as they approach the distal ex- 

 tremity of the lobe. 



The external surface is covered with glistening enamel, which is minutely furrowed. 

 The intervening ridges vary considerably in detail, both as to arrangement and form : in 

 some instances the ridges extend parallel with each side of the scale and meet at the 

 point, the successive ridges forming a series of triangles whose apices extend in a line 

 down the middle of the scale ; this is especially the case along the lateral surfaces of the 

 body. On other scales, especially along the ventral surface, the ridges extend more or 

 less along the axis of the scale, the longest being iu the middle, and becoming gradually 

 shorter on each side, and running out on the margins of the scale, giving it a some- 

 what jagged and rough outline. The ridges are not unfrequently broken by furrows 

 extending across them, and where this happens the surface has the appearance of 

 being covered with elongated tubercles. Various modifications of the several forms 

 described occur on the scales of a single specimen, and sometimes in close proximity one 

 to another (PL XLIX. fig. 3). 



The fins are supported in each instance, with the exception of the anterior dorsal fin, 

 by a pedunculate, lobate expansion of the teguments of the body. The lobes of the 

 posterior dorsal and the pair of ventral fins are large : in the specimen depicted on 

 PI. XLVI. they are quite half an inch in diameter ; those of the anal fin and the pectorals 

 are not so large. The anterior dorsal fin exhibits the ordinary arrangements of the fin- 

 rays, though they appear to be attached, in the specimen already referred to, without the 

 intervention of a lobe, apparently in close connexion with the neural spines. It is 

 impossible to distinguish the exact number of rays which compose each fin ; but twenty 

 rays may be counted fringing the extremity of the lobe of cither the dorsal or the ventral 

 fins, and it is probable that this number is fewer than actually exist, because the rays 

 are more or less folded and bent under each other. The pectoral and anal fins were 

 composed of a smaller number. The rays vary considerably in length : those springing 

 from the extremity of the lobe are an inch and a quarter to an inch and a half in length, 

 whilst those above and below gradually diminish, the sbortest being less than half an 

 inch in length. The basal portion of each fin-ray, for about two thirds the entire length, 

 is formed of a single bone pierced by a hollow tube, like the spinous bones of the body; 

 the remaining third is divided by numerous transverse jointings into small ossicles. 



The caudal fin is very large and powerfully built. The vertebral column extends in a 

 straight line from the body of the fish through, and some distance beyond, the caudal fin. 

 Its length beyond the extremity of the fin-rays shows a considerable amount of variation 

 in different specimens. In the one figured on PI. XLVIII. fig. 2 the vertebral prolongation 

 barely extends beyond the fin ; but in others, and in many instances smaller specimens, 

 there is fully an inch between the termination of the caudal-fin rays and the beginning 

 or basal portion of the smaller rays which form the second caudal appendage. Through- 

 out the whole length of the vertebral support for the second caudal fin there are small 

 rays on both the upper and lower surfaces, which appear to have served as a fin-like 



64* 



