NOTES ON AUSONIA COCKSII. 



165 



breadth of an inch ; the two outer ones only about an inch. In- 

 sertion of caudal fin crescentic, from which proceed 23 stout fin 

 raysj fin itself lineate, from point to point 17| inches, width 4 

 inches ; colour bright scarlet, with an external margin of blue, 

 which gradually becomes less distinct as it merges inwards. On 

 the under surface of the belly, at about 13 inches from the 

 chin, is the anal orifice, which is entirely protected by a single tri- 

 angular bony valve, which can be opened or closed at pleasure by 

 means of a cartilaginous disc which fulfils the purpose of a hinge. 



Ausonia Cocksii. 



From these external appearances alone, when contrasted with 

 those of Mr. Couch's Ausonia, it will be seen that the specific 

 differences are at once numerous and important. They may, I 

 consider, be thus briefly epitomized : — 



1. The heads are, I maintain, wholly dissimilar, whether 

 viewed from before, backwards, or in profile. 



2. The mouth, in the one case, is situated as in most of the 

 species ; in the other midway between the vertex and the lower- 

 most point of the gill coverts. 



3. The pectorals, in the one lanceolate ; in the other bluntly 

 triangular, with rounded margins. 



4. The spines and membranes on the dorsal and anal fins. 

 In my example the first spines in both are respectively 9 and 8 

 inches in length, just nine times as long as the others; whereas, 



f3 



