WORMS. 119 



ORDER II. MOLLUSCA. 



Naked simple animals, (, *Burnished with limbs. 



13. Actin i a. Body fixed by the base, warted, contractile, 

 with a single terminal mouth above surrounded by 

 numerous cirri. 



14. Ascidia. Body fixed by the base, smooth roundish, 

 apparently issuing from a sheath, with 2 terminal 

 apertures, one placed beneath the other, and radiate 

 with simple cirri. 



15. Derris. Body detached, cylindrical, composed of 

 articulations: mouth terminal: head with 2 simple 

 cirri at top. 



16. Holothuria, Body detached, cylindrical, open at 

 the extremity : mouth terminal, surrounded by 

 branched cirri. 



IT. Terebella. Body oblong, creeping, often inclosed 

 in a tube, furnished with lateral fascicles and bran- 

 chiae : mouth terminal, with lips but no teeth, pro- 

 truding a clavate proboscis, and surrounded by nume- 

 rous ciliate capillary cirri. 



18. Limax. Body oblong, creeping, with a fleshy shield 

 above, and a longitudinal flat disk beneath : aperture 

 placed on the right side, within the shield : feelers 4* 

 above the mouth, with an eye at the tip of each of the 

 larger-ones. 



19. Aplysia. Body creeping, covered with reflected 

 membranes, with a membranaceous shield covering 

 the lungs : aperture on the right side : vent above the 

 extremity of the back : feelers 4, resembling ears. 



20. Doris. Body creeping, oblongs flat beneath : mouth 

 placed below, on the fore-part : vent behind the back, 

 surrounded by a fringe : feelers 2 or 4, seated above 

 in front, retractile within their proper receptacles. 



21. Nereis. Body creeping, long with numerous la- 

 teral peduncles or feet each side ; feelers simple, 

 rarely none : eyes 2 or 4', rarely none. 



22. Aphrodita. Body creeping, oblong, covered with 



scales, and furnished with numerous bristly fascicled 

 feet each side: mouth terminal, cylindrical, retractile : 

 feelers 2, setaceous, annulate : eyes. 4. 



23. Amphitrite. Body projecting from a tube, annu- 

 late, furnished with numerous small feet each side : 



feelers 2, approximate, feathered : eyes none. 



24. Spio. Body projecting from a tube, jointed an^l-fur- 

 nished with dorsal fibres : peduncles or feet rough with 

 bristles and placed towards the back : feelers 2, long, 

 simple : eyes 2, oblong. 



