16 INTRODUCTION. 



back, and surrounded by a fringe ; feelers, two or 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 fur- 

 nished 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 an- 

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

 approximate, feathered ; no eyes. 



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

 enclosed in a tube, furnished with lateral fascicles or tufts, 

 and branchiae ; mouth placed before, furnished with lips 

 without teeth, and protruding a clavate proboscis ; feelers 

 numerous, ciliate, capillary, seated round the mouth. 



6. Nereis. — Body long, creeping, with numerous lateral 

 peduncles or feet, on each side ; feelers simple, rarely 

 wanting; eyes two or four, rarely none. 



7. AsciDiA. — Body fixed, roundish, and apparently issuing 

 from a sheath ; apertures two, generally placed near the 

 upper end, one beneath the other. 



8. Tethys Body detached, rather oblong, fleshy, with- 

 out peduncles; mouth with a terminal cylindrical proboscis, 

 under an expanded membrane or lip; apertures two, on the 

 left side of the neck. 



9. Triton Body oblong; mouth with an involute spiral 



proboscis ; tentacula or arms, twelve, six on each side, 

 divided nearly to the base, the hind-ones cheliferous. 



10. Sepia. — Body fleshy, receiving the breast in a sheath, 

 with a tubular aperture at its base ; arms eight, beset with 

 numerous warts or suckers, and in most species two pedun- 

 culated tentacula; head short; eyes large; mouth resembling 

 a Parrot's beak. 



It is exclusively upon the shape of the shell, and not upon 

 the structure of the animal inhabitant, that the Linnaean 

 arrangement of Conchology is founded. 



In early periods, naturalists were in much doubt whether 

 to found their Conchological arrangements on the animal, 



