MOLLUSCA. 303 



surface. The shell on its back is also delicate and 

 vitreous, but very small, procumbent, of an oval form, 

 and resembles a single valve of a bivalved shell. In 

 common with the former species, I have noticed some 

 examples of this to be destitute of a dorsal shell; 

 although the fin to which it should have been attached 

 was perfect. 



It inhabits the same waters as C. vitrea. 



(Firola, Sp.) 



We obtained a solitary specimen of this Firola, (or 

 Carinaria without a shell,) in lat. 40 N., Pacific Ocean. 



It is five inches in length, and composed of the 

 same gelatinous semi-pellucid structure as the Carina- 

 riae above described. The anterior two-thirds of the 

 body is somewhat cylindrical; the posterior third is 

 flattened, and tapers to a point at the tail. The dorsal 

 fin occupies the centre of the back ; while the anal is 

 placed very near the tail. On the posterior portion of 

 the abdomen there is a deep fissure, conducting, appa- 

 rently, to an anal orifice. The surface of the body is 

 covered, on some parts, with small tubercles ; and a 

 row of soft spines occupies the posterior part, or ridge 

 of the back. The oval tube, or tongue, (which is formed 

 like the same organ in Carinaria,) and the fins, were 

 the only parts of the animal that displayed any motive 

 power. 



