GASTEROPODA PECTINIBRANCHIATA. 
365 
Fig. 180. — Coiiciiolepas peruvianu.'. 
foot, pointed behind, widened in front, where it is marked with two deep emarginations. The eyes are on the sides 
of the tentacula, near the base. There is no veil nor operculum. (MM. Reynaud, and Quoy and Gaymard have 
observed that, under certain circumstances, the hinder part of the foot is spontaneously amputated.) We recognize 
the Purpura, Brug., by its flattened columella, pointed at the base, and forming there, with the outer lip, a canal 
excavated in the shell, but not projecting. The species were scattered among the Buccina and Murices by Lin- 
naeus. Their snail is like that of Buccinum as now restricted. Some shells similar to Purpura but in which we 
notice a spine on the outer margin of the canal, form the genus Licorna, Montf. {Monoceros, Lam.) Others in 
which the columella, or at least the lip, is garnished, in the full-grown shell, with teeth that narrow the mouth 
constitute the Sistra of the former, and the Ricimila of Lamarck. The Concholepas, Lam., has also the general 
characters of the Purpura, but the aperture is so 
enormously large and the spire so inconsiderable, 
that the shell has the aspect of a Capulus, or of one 
of the valves of an Area. The emargination of the 
mouth has a small tooth on each side of it. The ani- 
mal resembles that of Buccinum, excepting in the 
foot, which is enormous in width and in thickness, 
and which is attached to the shell by a muscle in 
form of a horse-shoe, as in Capulus. There is a thin, 
narrow, horny operculum. A species from Peru 
{Buccinum concholepas, Brug.) is the only one known. 
Cassis, Brug. — Shell oblong ; the aperture oblong or 
narrow; the columella covered with a plate as in 
Nassa, and that plate grooved transversely as well as 
the outer lip : the emargination ends in a short canal, 
which is folded and turned up backwards, and to the 
left. There are often varices. [The shells are called 
Helmets by English collectors, and are in general 
remarkable on account of their great size.] The 
animal resembles that of Buccinum, but its horny 
operculum is toothed, that it may pass between the 
grooves of the outer lip. Some have the varix of this 
lip toothed externally near the emargination; and 
others have it plain. The Morio, Montf. {Cassidaria, 
Lam.) are separated from the Cassis because their 
canal is less abruptly curved back; and they lead 
us to certain of the Murices. The animal resembles 
a Buccinum also, but its foot is more developed. 
[Oniscia, Sowerby, is sufficiently distinguished 
from Cassidaria by its granulated inner lip, its very 
short, scarcely reflected canal, and its very singular 
general form, which is oblong or subcylindrical, with an obtuse 
apex. Strombus oniscus, Linn., is the type of the genus.] Terebra, 
Brug., have the mouth, the emargination, and the columella of 
Buccinum, but their spire is drawn out so as to be turriculated or 
subulate. [The species are numerous and beautiful.] The Subula, 
Blainv., is distinguished by some dilference in the animal, and by 
the existence of an operculum. 
The Cerithium, Brug., — 
Dismembered with good i-eason from the Murex of Linnaeus, 
Fig. 182.— Cassidaria cchinophora. hav6 a slicll with a turriculatcd Spire, an oval aperture, and 
a short but distinct canal 
curved to the left and back- 
wards. There is a veil on 
the head of the animal, two 
distant tentacula, having 
the eyes at the side, and 
a round, horny operculum. 
Many of them are found in a fossil state. 
IM. Brongniart has separated from Cerithium the Potamides, which, with the same form of shell, have a very 
short, scarcely emarginate canal, no sinus or gutter near the top of the right lip, and the exterior lip dilated. They 
-Cassis tuberosa. 
Fig. 183. — Ceritheum. 
live in rivers, or at least at their mouths ; 
than land or freshwater species. 
and some of them are fossil in formations where there are no other 
