GALLERY.] NATURAL HISTORY. 119 
generally regularly spiral, with a moderately-sized aper¬ 
ture. 
The family of Nipple Shells ( Naticidce) are peculiar for 
having a large foot, in which the hemispherical shell is im¬ 
bedded, and which is much produced in front, beyond its 
edge; the tentacles are small, sometimes obliterated, and 
the mouth is hid in a groove; the operculum is spiral. The 
eggs are deposited in a broad, expanded band, folded like a 
funnel, sunk in the sand on the sea shore; these bands have 
been described as a coral, under the name of Flu sir a are - 
nosa. The genera Natica and Nacca , which have a 
moderate mouth, have a large operculum; and Crypto¬ 
stoma , which has a very large mouth, has a very small oper¬ 
culum. 
The animals of the following families have usually a 
moderately sized foot. 
The family of Periwinkles ( Littorinidce ) have a free 
oval, spiral, or subspiral horny operculum ; the shells ge¬ 
nerally have a roundish mouth, and are not pearly within; 
some have a simple round mouth, with a concave inner lip, 
as the Liltorince and Assiminia. Lacuna differs in the pillar 
lip being flattened, and the axis pierced; Scalaria is re¬ 
markable for having a white shell, marked with numerous 
varices, and the whorls are often only united to one an¬ 
other by the projections of the varices, thus exhibiting 
what is the case with all shells, that they are only formed 
of a coiled up, gradually enlarging tube; the Turritellce 
are turreted, and the Melanice and Cerithia, which have 
also generally elongated turreted shells, usually have a 
more or less distinct groove or nick in the front of the 
mouth. The Telescopium and Pyrazi have an orbicular 
many-whorled operculum, and the Cerithia an ovate one. 
Some, as the Melanopses, have a nick quite like the 
Buccina; but they are easily known from the marine 
zoophaga by their structure and mode of life, which is 
passed in fresh water; their apices are generally eroded, 
and they are often covered with a dark olive periostraca. 
The Tristoma are peculiar for having a contracted mouth, 
and a tubular hole, like the Typhis , at the posterior angle 
of the outer lip. 
The family of Looping Snails ( Truncatellidce ) have an 
oval spiral operculum, and the same form of animal as the 
