114 AUTUMNS ON THE SPEY. 



compensate for this, their external covering was 

 like a coat of armour. Their bones in fact were 

 outside, sometimes in the form of hroad plates, at 

 others in a beautiful arrangement of closely-fitting 

 scales, all coated with enamel. This will account 

 for the preservation of the external form. The head, 

 as in osseous fishes, is of bone, but unlike the latter, 

 which is divided into a great number of distinct 

 parts, it generally consisted of a single piece 

 without any joint. It was therefore less liable to 

 decay, or at least to separation from the body, and 

 yet among the specimens in this collection, and 

 in those I subsequently procured myself in the 

 fish-bed of Tynet burn, the skull was decidedly 

 the least perfect portion of each, although in 

 many species it would appear to have been pro- 

 tected by a continuation of the enamelled armour. 

 But the most striking distinction between the 

 cartilaginous and the ordinary osseous fishes, is in 

 the form of the tail. The latter, as you know, 

 like the salmon, herring, cod, or mackerel, and 

 even the flat turbot or sole, possess a tail com- 

 posed of two equal parts ; set on, as it were, at 

 the end of the vertebral column. Not so among 

 the cartilaginous fishes. With them it is formed 

 on both the upper and lower portion of the spine. 

 In fact, the body, gradually attenuated as it 



