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CONCHOLOGY. 



Shell. Thin, fragile, papyraceous, spiral, the whorls reunited 

 in a planorbis form, and deeply and largely umbilicated on one 

 side, aperture large and entire. Inhabits the north seas. One 

 species. 



Limacina helicialis. 



5. Genus Cymbulia. 



Animal. Body oblong, gelatinous, pellucid, enclosing a shell ; 

 head sessile; two eyes, and two retractile tentacula; mouth with 

 a retractile proboscis ; two opposite oblong ovate, branched wings, 

 connate at their posterior base. 



Shell. Gelatinous, cartilaginous, very transparent, crystalline, 

 oblong, in shape of a shoe, from which it has derived the name 

 of the slipper, truncated at the summit ; aperture lateral and ante- 

 rior. Inhabits the Mediterranean. One species. 

 Cymbulia Peronii. 



6. Genus Pnexunodermon. 

 A Molluscous animal, whithout any testaceous covering, and 

 much resembling the genus Clio. Inhabits the Indian seas. One 

 species. 



Pneumodermon Peronii. 



FAMILY II. 



PflTLLiniACEA. Six genera. 



1. Genus Phyllidia. 

 A mollusca similar to the preceding genus, without a shell, but 

 its back covered with a rough or coriaceous skin. Inhabits the 

 Mediterranean. Three species. 



Phyllidea varicosa. Phyllidea pustulosn. 



P. ocellata. 



2. Genus Chitonelhis. 

 Animal. Body creeping, elongated ; middle of the back pro- 

 vided its entire length with a detached multivalve shell ; the 



