420 THE OCEAN WOBLD. 



species. Such are Cerithium fasciatum (Fig. 244) and Cerithium 

 aluco (Fig. 245). 



The Giant Cerithium, Cerithium giganteum (Fig. 246), is the liv- 

 ing analogue of a magnificent fossil species belonging to the tertiary 

 formation. The single known example of this species belongs to the 

 Delessert Museum at Paris. A manuscript note by Lamarck, attached 

 to this specimen, relates that this shell was first brought to Dunkirk 

 in 1810 by an Englishman, one of the crew of an English ship. 

 The English sailor had drawn it up from the bottom of the sea with 

 the sounding-lead from a bed of rocks off the coast of Australia. 



The fourteenth family, Pyramidellidte, contains Chemnitzia and 

 Pyramidella, extremely pointed shells. 



The fifteenth family, Naticidse, contains Lamellaria and Natica ; 

 the last of which is found in most seas. 



The second section of the Prosobranchiata is termed Siphono- 

 stomata, which are characterized by a spiral imperforate shell, the 

 animal of which has sometimes a horny operculum, and is furnished 

 with an elastic trunk, the margin of the mantle acting as a siphon. 

 They are carnivorous. 



The first family is the Cypreeidse, containing the well-known 

 Cyprsea and Ovulum. 



The Cowries, or Cypr&a, are brilliant, smooth, and polished, oval- 

 shaped, or oblong convex, with edges rolling inwards and longitudinal 

 openings, narrow, arched, dentate on both edges, and notched at the 

 extremities. The spiral, placed quite posteriorly, is very small, and 

 often hidden by a calcareous bed of a vitreous appearance. 



It is now known that the form and colouring of the shells vary 

 very considerably, according to the age of the animal : so much so, 

 indeed, that the same species examined at various stages of its growth 

 would almost seem to belong to species and even to genera essentially 

 different. 



The young cowries are thin, conical, elongated ; with conspicuous 

 spiral, and large openings. The right edge soon becomes thicker, 

 and folds itself inwardly ; the opening is narrowed ; finally, the 

 spiral is unfolded in successive folds from the right edge, and by 

 successive deposits of the vitreous matter we have spoken of the 

 opening is gradually contracted, its extremities hollowed out, its edges 

 disconnected, and the shell, until now only shaded in pale tints, 



