302 ZOOLOGY. 



vitreous shell, of small size, perfectly transparent, and 

 shaped like a cornucopia. Some few examples of the 

 same species, which we obtained, were destitute of this 

 shell ; and their naked dorsal fin bore no appearance of 

 its having been recently present. I have also found 

 the shell alone, floating empty on the surface of the 

 sea. 



When the shell is present, the portion of dorsal fin 

 contained within it has a black hue ; * and is covered 

 with a continuation of the same membrane that invests 

 the entire body of the animal ; while the shell is so 

 firmly attached to its surface that it cannot be re- 

 moved without injury to its structure. But it is re- 

 markable, that in those instances where the shell did 

 not exist, the dorsal fin, though perfect, was as colour- 

 less, and of the same consistence, as the body and anal 

 fin. I was at first inclined to believe that this shell 

 was a parasite; but its uniform shape in the same 

 species of Carinaria, and the circumstance of its being 

 invariably attached to the same part of the body, in- 

 duced me to fall into the opinion of naturalists, that 

 it is identical with the perfect structure of this 

 mollusc. 



Some living specimens which we obtained, and put 

 into a pan of sea-water, swam horizontally, with a quick 

 lateral motion of the dorsal and anal fins, and rose to 

 the surface or descended with great ease. 



(Carinaria Depressa, Cuvier.) 



This species is about the size of the former; but its 

 body is broad and flat, and tuberculated on its dorsal 



* This black structure is said, by Cuvier, to consist of a nucleus, 

 formed by the heart, liver, and genital organs. 



