386 REMARKS ON THE GENUS SCISSURELLA. 
(most conspicuous in the spaces), giving to the shell its pe- 
culiar reticulated appearance. The ribs on the upper side 
are coarser than those below. The aperture is suborbicu- 
lar, slightly depressed ; the outer hp thin, the inner lip 
slightly reflected over the cavity, spread on the body 
whorl, and continuous with the outer lip. From the pil- 
lar cavity a shallow gutter extends anteally, and shortly 
joins the pillar lip. It is chiefly conspicuous on the larger 
specimens. The longitudinal slit, in the middle of the 
outer lip, extends backwards about two-thirds of the dia- 
meter of the shell, when it joins the narrow groove in the 
keel of the shell which had formerly been occupied by the 
slit. The margins of the slit are slightly elevated, as well 
as the groove, which is seen winding round at the separa- 
ting line nearly to the apex. The groove itself is slightly 
ribbed across. 
It seems probable, that the slit is situate immediately 
over the aerating organs of the animal. All the specimens, 
when found, were destitute of the animal, thus preventing 
any observations on its forms ; but, from the number of 
shells collected in one spot, it would appear to be gregarious 
in its habits. 
The preceding description offers one statement which 
would seem to forbid the insertion of this shell in the ge- 
nus S issurella of M. D'Orbigny, — the continuous peri- 
stome. In the generic character, the lips are represented 
as disjoined. Whether this may lead to the institution of 
a new genus, when a greater number of recent species 
shall have been detected, or when the fossil species, of 
which Mr Sowerby, we believe, possesses several examples, 
shall have been described, we do not venture to determine. 
M. D'Orbigny describes two recent species. The first, 
Scissurella l(jevigata^ is smooth, or marked only by the 
lines of growth. The second, Scissurella costata, is rib- 
1 
