493 



CYVRMABM. 



Of this group, remarkable for the exquisite beauty of 

 its shells, we have but few, and those comparatively insig- 

 nificant representatives, in our fauna. The majority of 

 species in the tribe are inhabitants of the tropics, where 

 their brilliant colours and polished surfaces accord better 

 with light and warmth. The shells of all the genera are 

 involute, and usually have but small spires. Their aper- 

 tures are canaliculated for the passage of a well-developed 

 siphonal process. Their surfaces are often highly polished 

 and porcellanous, exhibiting no traces of an epidermis. The 

 animal has large lateral lobes, often brightly coloured and 

 variously ornamented, which it reflects upon the shell. Its 

 head is intermediate in form and parts between those of 

 the groups of gasteropoda, with a retractile proboscis, and 

 with a muzzle. The dentition approximates the C^/pr^ada 

 to the latter section. There is but one branchial plume. 

 The individuals are bisexual. There is no operculum. 



The difference of aspect between these mollusks when 

 crawling, with all their beautifully coloured soft parts ex- 

 posed, often completely concealing their enamelled shells, 

 and their appearance when, after being seized, they sud- 

 denly and instantaneously withdraw their bodies and 

 mantle-lobes and expose the shell only, is very curious and 

 surprising. 



