4 23S MOLLUSCA. 



CLIO, Linnaeus. 



Body oblong, membranous, without a mantle; head formed of two rounded 

 .lobes, whence originate small tentacula; two small 

 fleshy lips, and a little tongue on the front of the 

 mouth; the fins covered with a vascular net- work 

 which acts as branchia?. Some authors consider them 

 as possessing eyes. 



Clio borealis, Lin. This species, which is the most celebrated, is found in 

 astonishing numbers in the Arctic Seas, furnishing, by its abundance, food for 

 the whales, although each individual is hardly an inch long. 



CYMBULIA, Peron, 



A cartilaginous or gelatinous envelope, resembling a galley, or rather a sabot 

 or wooden shoe, bristling with small points disposed in longitudinal rows. 

 The animal has two large wings composed of a vascular tissue, which are its 

 branchiff and fins ; between them, on the open side, is a third and smaller 

 lobe with three points. 



PNEUMODERMON, Cuvier. 



The Pneumoderma begin to be a little further removed from the Clios. Their 

 body is oval, without a mantle and without a shell ; the branchia; are attached 

 to the surface and composed of little laminse arranged in two or three lines, so 

 disposed as to form an H on the part opposite to the head. 



LIMACINA, Cuvier. 



The body terminates in a spirally convoluted tail, and is lodged in a very thin 

 shell formed by one whorl and a half, umbilicated on one side, and flattened 

 on the other. The animal uses its shell as a boat, and its wings as oars, 

 whenever it wishes to navigate the surface of the deep. 



Clio helirina. Almost as common on the Arctic Seas as the Clio borealis, 

 and is considered as forming the chief source of food for the whale. 



There are three other genera in this class, Hyalea, Cleodora, and Pyrgo, a 

 very small fossil shell. 



CLASS III. 



GASTEROPODA. 



THE Gasteropoda constitute a very numerous class of the Mollusca, 

 an idea of which is afforded by the Slug. 



They generally crawl upon a fleshy disk, situated under the abdo- 

 men, which sometimes however assumes the shape of a sulcus, or that 



