CHITONIDiE. 467 



Genus NACELLA, Schumacher. 



Mouth entire below ; gills interrupted in front of the 

 head, and ending nearly symmetrically on each side of 

 the neck. 



Shell thin, semi -pellucid, cap-shaped, surface smooth j 

 apex anterior, recurved, nearly marginal ; aperture wide, 

 oval, internally opalescent, margin simple, entire. 



Syn. Patina, Leacli. Ansates, Sow. jun. 



Ex. N. pellucida, LimKBus, pi. 52, fig. 10. Shell, N. 

 cymbalaria, Lamarck, fig. 10, a. 



The " Sea-weed Limpets " are readily distinguished 

 from the " Rock Limpets " even by their shells, which are 

 smooth, thin, sharp-edged, and cap-shaped. They are 

 usually found parasitic on sea-weed, adhering to the fronds 

 or even imbedding themselves in the parenchyma of the 

 stalks, as N. insessa, and a variety of A^. pellucida on our 

 own shores. Species of Nacella are inhabitants of the 

 British Islands, the Cape of Good E[ope, Cape Horn, and 

 Australia. 



Species of Nacella. 



cterulea, Linn. insessa, Hinds. 



cymbalaria, Lam. pellucida, Linn. 



Delessertii, Phil. plumbea, Lam. 



depicta, Hinds. radians, Gmel. 



hyalina, Phil. vitrea, Phil. 



Fam. CHITONIDJE. 



Lingual riband long and linear, furnished with nume- 

 rous transverse series of teeth ; three central or rachidian. 



