366 MOLLUSCA. FISSURELLADJE. Scissurella. 
3. E. tricarinata — Conical, with the apex bent down ; surface marked with 
three principal, and several lesser ribs, the spaces between them nearly 
smooth ; base oblonff. — Sower. Min. Conch, t. Dxix. f. 2 In Oolite at An- 
cliff. 
4. E. scalaris — Conical, ribbed ; apex excentric ; ribs many, connected by 
numerous cross lines ; base obovate — Sower. Min. Conch, t. Dxix. f. 3 In 
Oolite at Ancliffe. 
Gen. XC. SCISSURELLA. — Shell with a depressed spire ; 
the outer-lip notched with a deep sliL following the 
growtli of the volutions, obliterated to within a short dis- 
tance of the margin, and forming a sort of keel upon the 
back of the shell. 
365. S. Transversely ribbed, and spirally striated ; 
inner- lip reflected on the body-whorl. 
In shell-sand at Noss, Zetland, after a storm. 
Breadth about the fifteenth of an inch ; white, and without any apparent 
cuticle : whorls three, increasing rather rapidly from the slightly elevated 
apex, and sloping, with a gentle convexity, from the separating line to the 
keel ; under side with a central cavity, from which the whorl extends, a lit- 
tle convex, to the keel. The whorls are marked by numerous fine trans- 
verse arcuated ribs, narrower than the intervening spaces, crossed by fine 
longitudinal striae (most conspicuous in the spaces), giving to the shell its 
peculiar reticulated appearance ; the ribs on the upper side are coarser than 
those below. The aperture is suborbicular, slightly depressed, the outer-lip 
thin ; the inner-lip slightly reflected over the cavity, spread on the body- 
whorl, and continuous with the outer-lip. From the pillar-cavity a shallow 
gutter extends anteally, and joins the pillar-lip ; this is chiefly conspicuous 
on the largest specimens. The longitudinal slit in the middle of the outer- 
lip extends backwards about two-thirds of the diameter of the shell, where it 
joins the narrow groove in the keel of the shell which it had formerly occu- 
pied. The margin of the slit is slightly elevated, as well as the groove, 
which is seen winding round the whorls at the separating line, nearly to the 
apex ; the groove itself is slightly ribbed across — I found this shell in 1809, 
and specimens then transmitted to Mr Montagu, were pronounced by him 
the fry of a Trochus. It is, however, a well marked shell, and belongs to 
the genus Scissurella of M. D’Orbigny. 
1 
