NATURAL HISTORY. 
57 
GALLERY.] 
Phorcus the axis is deeply umbilicated. In Ziziphinus, Cantharidus 
and Thalotia, the mouth is oblong and simple, and the axis of the shell 
is covered by the inner lip; the former is top-shaped, the Cantharidi are 
ovate and green within. The Gibbium have a depressed top-shaped 
. shell with perforated axes. The Rotella chiefly differ from them in the 
axis being covered with a thick callosity. The Monodonta are ovate 
thick shells, with a tooth on the inner lip, and have usually an opake 
white rib within the pearly mouth. The Talopia are like the Rotella, 
the shell is striated and umbilicated, the umbilicus being edged with a 
striated callous edge, which in Camitia is so large as nearly to hide it. 
The Margarita are like Gibbium , but thin and pearly. The Livonce 
are solid conical shells with a roundish mouth and a callosity partly 
covering the umbilicus. The dolphin shells ( Delphinula ) differ from 
all the rest in being thick turbo-like umbilicated spinose shells with a 
round mouth; and the Liotia differs from Delphinula in having a 
regular margined mouth to the shell. 
The family of Stomatellas ( Stomatellid^e, Case 18) are very like 
the former, but the mouth of the shell is large and expanded compared 
with the size of the spire and operculum. The Stomatellce have a thick 
depressed shell with a roundish mouth and a distinct operculum, and the 
Gence are thin, oblong, ear-shaped shells, with a very large animal and 
no operculum. 
The family of Ear-shells (Haliotlele, Case 18) have even a more 
expanded mouth than the former; they have no operculum, and the side 
of the foot of the animal is covered with a hard warty skin ; but their 
most peculiar character consists in their having usually a groove or slit 
in the mantle, over the part where their gills are situated. In Stomatia 
the place of this slit is marked in the shell by a groove, while in Haliotis 
and Padollus the groove of the shell is pierced with a series of holes in 
front, which are gradually filled up behind as new ones are required to 
be formed by the growth of the animal, the last being occupied by the 
vent. Padollus chiefly differs from the former in there being a groove on 
the shell, rather behind the series of holes. Deridobranchus has a large 
thick shell, like Haliotis , which is entirely sunk in and covered by the 
thick hard plaited mantle of the animal. The Ralia have a thin an¬ 
gular ( fossil ) shell, like Janthina , with a central notch leaving a broad 
groove on the keel of the last whorl, and in Scissurella and Pleuroto - 
maria there is a long slit in the shell, over the opening in the mantle. 
The former are very minute thin shells, with a small spire and a large 
mouth with the slit interrupted near the edge. The latter are top¬ 
shaped (fossil) shells, having an enlarged spire and an oblong four-sided 
mouth; they have been confounded with the Trochi. 
The family of the keyhole limpets (Fissurellim:, Case 18) have an 
animal very like the ear-shells, but the shell is depressed, simply conical, 
not pearly, and furnished either w ith a hole, placed in the front of the 
apex, as in Fissurella , or with a notch in the front of the edge, as in 
Emarginula and Parmophorus. These holes or grooves afford a pas¬ 
sage for the w^ater to the respiratory organs, and for the expulsion of the 
feeces. In Parmophorus the shell is solid and the front edge is only 
arched, in Emarginula the shell is thin and cancellated, and there is a 
regular notch or slit in front. The Diodorce, like the young Fissurella , 
have the hole in the front of the apex, but unlike them the apex is not 
