186 PECTINIBRANCHIATA.—NATICADA. 
ever, exclusively marine, and generally inhabits 
deep water. It is an open-mouthed shell, about 
half an inch in diameter, of a dull reddish hue, 
covered with a furry epidermis. Messrs. Forbes 
and Hanley distinguish it from its fellow species 
by affirming that it is not membranaceous, but this 
does not agree with my own experience; the 
specimens that have fallen under my notice having 
been quite flexible and membranaceous, especially 
near the margin. Nothing is known of its habits. 
Famity NATICcADé. 
(Naticks.) 
The shell in this family is globose, with the 
spire minute and scarcely raised; the surface is 
generally smooth, and often covered with a porce- 
lain-like polish; the aperture is large and semi- 
circular; the pillar is always thick and solid, and 
its exposed part, constituting what is technically 
known as the inner lip, is often very broad. 
The animal is large in proportion to the shell, 
yet capable of being wholly withdrawn into it. 
The mouth is not extended into a proboscis, but is 
concealed beneath a broad hood or veil. When 
the eyes can be recognised, they are placed at the 
bases of the tentacles. The mantle is entire, that 
is, its edges are not cut into filaments. An oper- 
culum is always present, sometimes horny in 
texture, sometimes shelly, but invariably closing 
the wide aperture of the shell. 
Though the genera comprised in this family are 
few, the constituent species are numerous, and 
widely scattered in geographical distribution. For 
