NATURAL HISTORY. 
61 
GALLERY. ] 
produced in front. Mesalia is very like the former, but the mouth is 
round and produced into a slight canal in front, and the front of the 
inner lip is slightly twisted. Eglisia has a round mouth with the outer 
lip rather thickened internally. The Eulimas are like the Turritellcs, 
but the shells are solid, opaque white, internally variced, and polished, 
and Nisso differs from them in being umbilicated. The Melanias, 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. 
They are all fluviatile, or only found at the mouth of rivers where the 
water is brackish, and they are covered with a hard black periostraca 
on the surface, and are often eroded; sometimes the tips are quite de¬ 
stroyed, the cavity of the shell being filled up at top as the apex is eroded. 
The Melanias have an ovate entire mouth, with a thin outer lip to the 
shells, and an ovate operculum. The Tiaras differ in having an ovate 
shell. Pachystoma differs in the outer lip being variced. The genera 
Tania, Anculosa, and lo have the mouth of the shell truncated in front 
of the axis, as in Achatina; the former having a turreted, the second 
an ovate short, and the latter a fusiform shell with a large mouth. The 
Melanopses and the Pyrenes have a nick quite like the Buccina; but 
they are easily known from the marine zoophaga by their structure and 
mode of life. The Cerithiums have a more or less distinct recurved 
canal, and indistinct varices, like some of the Tritons , but their outer 
lip is rather expanded, which induced the older conchologists to place 
them with the Strombs. The genera Cerithium and Vertagus have an 
ovate operculum like the Melanias . The Pot amides, Telescopium and 
Pyrazus have a rounder mouth to the shell and an orbicular many- 
whorled operculum. Tristoma differs from the latter in having a con¬ 
tracted mouth, and tubular hole, like the Typhis, at the posterior angle 
of the outer lip. Vibex and Ceriphasia differ from Cerithium in having 
only a very slight groove-like canal. They have an ovate operculum. 
The family of Looping Snails (Truncatellidje, Case 20) have an 
oval spiral operculum, and the same form of animal as the former family, 
but thefoot is small, and the lips very large and expanded ; the animal 
walks by contracting the space between these parts into a loop, like the 
Looper or Geometric Caterpillars. 
The family of Pond Snails, (Paludinhle, Case 21,) like the Am- 
pullariadas, and unlike the other families of this group, are fresh water 
Mollusca, with the opercula formed of regular rings, but they differ from 
the Ampullariadas in having short tentacles, sessile eyes, and an entire 
forehead. The Paludincs have a horny operculum, and are ovovivipa- 
rous, while the Bithinios , which have a shelly operculum, are oviparous,, 
like Lymnasa. Meladomus are like Paludincs, but sinistral. CUtjvd* » 
The family of Velutinim: (Case 21) have an animal very like the 
Littorinidcs, but they are destitute of any operculum, and the shell is 
small for the size of the animal, with a very short spire and a large 
mouth. They live on stones on the sea shore. 
The family of Pyramid Shells ( Pyramidellid^e, Case 21) are at 
once known by the oblique plaits on the front of the pillar lip of the 
polished, spotted, turreted shell, and by their tentacles being broad and 
folded like the ears of a hare ; they have the eyes at the inner side of 
their base, like the Auriculae; their operculum is horny, with a flap on 
the inner side to adapt it to the plaits on the pillar. The genus Odos - 
