204 



POPULAR CONCHOLOGY. 



The Mollusca which form these shells are very trans- 

 parent, but are possessed of lively and brilliant colours ; 

 they only appear on the surface of the sea during calms. 

 The shells are comparatively small, as they only cover the 

 circulating and respiratory organs; they were formerly 

 very rare (specimens having been sold for one hundred 

 guineas), but are now more common: they are seldom 

 perfect. 



Cardiopoda. UOrb. — No shell Animal fusiform, 

 the head very thick, not distinct; two tentacula before 

 the eyes ; a stalked nucleus without shell, but which in 

 form resembles the embryo whorls of the Carinaria. — 

 2 species. 



Found in the Atlantic. 



Ceratophora. UOrb. — No shell. Animal, with a 

 fusiform body, with distinct head, and two long tentacula 

 before the eyes ; the nucleus naked. — 1 species. 



From the Pacific Ocean. 



Pterotrachea. Forskal. (Firola Peron and Les. ; 

 Hypterus Ralin.) — Animal fusiform, with a distinct head, 

 which is prolonged into a pointed snout, at the end of 

 which is the mouth ; the eyes, very perfectly organised, 

 are at the base of the head; no tentacula, but in their 

 place a pair of small points (rudimentary) before the eyes ; 

 the nucleus (intestines, &c.) naked, unstalked, and pear- 

 shaped. — Many species. 



From the Mediterranean, Atlantic, and Pacific Oceans. 



Family 2.— ATLANTA CE A. 



The body of the animal can be withdrawn entirely into 

 the shell, which is spiral-formed ; besides the fin there is 

 a distinct foot ; the comb-formed gills are situated under 

 the mantle. 



