Peering into the deep and narrow fissures with which the rocky ledge
is cleft, we observe some shells which properly belong to the deep
sea bottom, but have been doubtless washed into the shallow, by some
heavy ground-swell, and left where we now see them. Here are several
fragments, and one or two nearly perfect specimens, of what looks like
an elephant’s tusk in miniature, but is really the shell of a small
Gastropod mollusk commonly known as the Tusk-shell.[72] In colour,
form, and curvature, the resemblance is complete, but the length of a
perfect shell rarely exceeds an inch and a half, with a diameter of
one-eighth of an inch at the larger end. The animal is remarkable for
having long been a subject of dispute with learned zoologists as to
its true affinities; by some being considered as a true mollusk allied
to the Limpets, by others as a worm allied to the _Serpulæ_. Anatomy
determines it to be rightly located by the former opinion, and yet the
possession of red blood, and some other peculiarities belonging to the
_Annelida_, indicate a curious relationship with this class, so that we
may consider it as one of those interesting forms which link together
two great divisions of the animal kingdom.
[Illustration: