MOLLUSCA OK UNIVALVES. 137 



on the upper part of the head. — 7 species 

 recent. 



These mollusca inhabit the sea, where they 

 are seen in calm weather and during the hottest 

 part of the day. They appear and disappear 

 continually on the surface. Found in the seas 

 of the Cape of Good Hope, India, and the 

 Northern Atlantic. 



3. Cleodora. — Shell gelatinous, cartila- 

 ginous, transparent, in the shape of 

 a reversed pyramid, truncated, and 

 open at the summit. Animal, body 

 oblong; head distinct, having two 

 eyes ; no tentacula. — 11 recent and 

 2 fossil species. 



The Indian and Atlantic Oceans produce 

 these curious animals. 



4. Limacina. — Shell thin, fragile, papy- 

 raceous, and spiral; the whorls 

 discoid or flattened. Animal, body 

 long, and greatly resembling the Clio. — 1 

 species recent. 



The animal can retire completely into its 

 shell. It inhabits the Northern seas ; and is said 

 to be devoured by whales in vast quantities. 



