41 
P1LE0LUS, G. B, Sowerby. 
Gen. Char. Shell conical, with a subcentral, 
upright vertex ; base concave, with a thin 
margin and tumid centre; aperture small, 
within the margin of the base, sublateral, 
semilunar, its outer lip prominent, the 
inner one crenulated ; spire internal, very 
short. 
The form of the upper surfaces of the shells of this 
Genu9 is similar to that of Patella, for it is a short cone, 
from the apex of which there are sometimes diverging 
striae or ridges ; the base also resembles Patella, in as 
much as that it has a thin or sharp edge. Within this 
edge is seen the transverse aperture leading to a very 
short spire, that is wholly included within the cone, and 
nearly fills it up in the form of a cushion. The aperture 
is slightly curved and narrow, with parallel lips, and 
rounded extremities ; the lips are separated, that near- 
est the centre is crenulated. We suspect the spire is 
reversed. 
The wholly internal spire, and the prominent outer 
lip of the aperture, independent of the margin of the 
base, are characters not possessed by any other genus of 
involute shells. There are several points of resemblance 
Vol. V, 
