INTRODUCTORY. 1.5 



eludes the genera Conus, Cyprcea, Voluta, &c., of the Linneau 

 arrangement. 



The second class consists of shells generally covered with a 

 strong epidermis or skin, below which lies the shell in layers, 

 and composed entirely of the substance well-known by the name 

 of mother-of-pearl. In this class are the fresh-water Mus- 

 cles, (the Mytilus Cygneus and Anatinus of Linne,) the 

 Haliotis or ear-shells, the Turbo, and several of the Trochus 

 tribe, &c. 



The porcelaneous shells, contain a very small portion of soft 

 animal matter, and those of the second class a very large propor- 

 tion.* 



Shells, therefore, are only the habitation of soft animals called 

 Vermes, or Worms, which constitute the third order of Linnjeus's 

 sixth class of animals. According to that author, the animals 

 have been aiTanged into ten genera, as follow : 



1. Limax ; 2, Doris ; 3. Spio ; 4. Amphitrite ; 3. Terebella ; 

 6. Nereis ; 7. Ascidia ; 8. Tethys ; 9. Triton ; 10. Sepia. 



1. Limax. — Body oblong, creeping, with a fleshy kind of shield 

 above, and a longitudinal flat disk beneath ; aperture placed on 

 the right side, within the shield ; feelers four, situate above 

 the mouth, and an eye at the tip of the largest ones 



This genus is what is generally termed the slug, or snail. 



2. Doris. — Body, creeping, oblong, and flat beneath ; mouth 

 placed below, on the fore-part ; vent behind, on the back, and 

 surrounded by a fringe ; feelers, two and four, seated on the 

 upper part of the body in front, and retractile within their proper 

 receptacles. 



3. Spio. — Body projecting from a tube, jointed and furnished 

 with dorsal fibres ; peduncles, or feet, rough with bristles and 

 placed towards the back ; feelers two, long, simple ; eyes two, 

 oblong. 



4. Amphitrite.— Body projecting from a tube and annulate ; 

 peduncles, or feet, small, numerous ; feelers two, approximate, 

 feathered ; no eyes. 



5. Terebella. — Body oblong, creeping, naked, often inclosed 

 in a tube, furnished with lateral fascicles, or tufts, and branchice ; 

 mouth placed before, furnished with lips without teeth, and 



• See Thomsoa's System of Chemistry, Vol. V. p. 507. 



