66 CLASS GASTEROPODA. 
CREPIDULA, Lam. 
The shell oval, with an obtuse horizontal point, directed ob- 
liquely backwards and laterally, the aperture forming the base 
of the shell, which is half closed beneath, and behind with a 
horizontal plate ; the abdominal sac which contains the viscera 
is on this plate, the foot beneath, and the head and gills for- 
wards: the latter consist of a range of long filaments, attached 
under the anterior margin of the branchial cavity ; the eyes 
are at the external base of two conical tentacula, (Patella 
fornicata, List. 545. 33. 35, &c.) 
PILEOLUS, Sowerby, 
Appears a crepidula, in which the transverse plate occupies 
half the aperture; the shell, however, is more like that of a 
patella. (Pileolus plicatus, Sowerb.) ‘They are only found 
fossil. 
SEPTARIA, Fér. NAVICELLA, Lam. 
CIMBER, Mont., 82. 
The shell resembles a crepidula, except that the summit is 
symmetrical, and laid on the posterior margin, and that the 
horizontal plate is less salient. ‘The animal is also provided 
with an additional irregularly shaped testaceous plate, attached 
horizontally to the superior surface of the muscular disk of its 
foot, and covered by the abdominal sac, which it partially 
supports. It is probably analogous to an operculum, but 
does not exercise its functions, being, in a measure, situated 
internally. The animal has long tentacula, at whose external 
base are pedicles which support the eyes. They inhabit the 
rivers of hot countries. (Patella neritoidea, List. 545. 36, &c.) 
CALYPTREA, Lam., 
Have a conical shell, in the hollow of which is a little lamina 
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