NATURAL HISTORY. 
21 
GALLERY.] 
in having a well-developed horny operculum and more regularly- 
formed gills. 
The family of Cerithiopsidce have seven rows of teeth on the tongue, 
and a turreted shell like the Cerithia or Marsh Shells, but the animal 
has an elongated proboscis and is carnivorous, and in its habit and 
appearance resembles the species of the next family. 
The family of Pyramid Shells {Pyramidellidce) have an elongated 
tongue-membrane, which is destitute of any teeth. The tentacles are 
often doubled or folded like the ears of a hare, and the first whorl of 
the young shell, which forms the top of the full-grown one, is placed 
across the others or bent in a different direction to them. They are 
generally small turreted shells. 
The Stair-case Shells {Architectona) have an animal very like the 
former, but the shell is depressed with a large central cavity like a 
spiral stair-case, or nearly flat. 
Table 14 to 20 contain the shells of the Rostrum-bearing Molluscs 
( Ttostrifera), which have an elongated corrugated muzzle bearing the 
tentacles on the sides. They have seven rows of teeth on the tongue- 
membrane. They are divided according to the form of the foot and 
the position of the eyes. 
Table 14 to 18. The shells of those families which have a broad 
expanded foot by which the animal crawls from place to place. 
.^able 14. The Apple Snails {AmpullariadcB), which have pe- 
duncled eyes on the outer side of the base of the elongated tapering 
tentacles, and the front of the forehead deeply bifid, and divided into 
two elongated subulate lobes like the tentacles. They live in ponds in 
warm climates; the operculum is annular. In all the other families 
the eyes are sessile at the base of the outer side of the tentacles. 
Tables 14 and 15 contain the Egg Shells {Amphiperacidce), the 
Cowries {CyprceadcB), the Coral or Bug Shells {Pedicularidce), and 
the Pelican’s Foot Shells (^Aporrhaidce), which have a distinct siphon 
on the front of the mantle, a canal for its protection in the front of the 
shell, and the mantle of the shell more or less produced, so as to cover 
the shell, or form an expanded outer lip to the shell. 
Table 15 contains the families of Terrestrial Mollusca belonging to 
this group which have the gills in the form of vessels spread over the 
inner surface of the open gill-cavity. They have been confounded 
with the Pneumohranchous Mollusca, but they differ from them in 
being unisexual, in the structure of the tongue, and in the respiratory 
cavity not being a close cavity, as the families Cyclophoridce, Helici^ 
nidce, and ProserpinidcB. 
Tables 16—18. The shells of the families which have an external 
spiral shell with a contracted mouth, an enclosed mantle without any 
distinct siphon for conducting the water to the gill-cavity, and a mode¬ 
rate-sized foot, as Littorinidce, Pissoadcc, Melanidoe, Viviparidce, 
Valvatidce. 
Table 18. The families which have an exposed expanded shell 
with a large aperture, the mantle of the shell enclosed. They have a 
large expanded foot and no operculum. These animals live a seden¬ 
tary life, seldom changing their place. The eggs are usually attached 
to the under side of the foot, and the under side of the foot sometimes 
