"C. tuberculatum," says Mr. Gosse (who described it from specimens
which I sent him in 1854), "is far the finest species. The valves
are more globose and of a warmer colour; those that I have seen are
even more spinous." Such may have been the case in those I sent:
but it has occurred to me now and then to dredge specimens of C.
aculeatum, which had escaped that rolling on the sand fatal in old
age to its delicate spines, and which equalled in colour, size, and
perfectness the noble one figured in poor dear old Dr. Turton's
"British Bivalves." Besides, aculeatum is a far thinner and more
delicate shell. And a third species, C. echinatum, with curves
more graceful and continuous, is to be found now and then with the
two former. In it, each point, instead of degenerating into a
knot, as in tuberculatum, or developing from delicate flat briar-
prickles into long straight thorns, as in aculeatum, is close-set
to its fellow, and curved at the point transversely to the shell,
the whole being thus horrid with hundreds of strong tenterhooks,
making his castle impregnable to the raveners of the deep. For we
can hardly doubt that these prickles are meant as weapons of
defence, without which so savoury a morsel as the mollusc within
(cooked and eaten largely on some parts of our south coast) would
be a staple article of food for sea-beasts of prey. And it is
noteworthy, first, that the defensive thorns which are permanent on
the two thinner species, aculeatum and echinatum, disappear
altogether on the thicker one, tuberculatum, as old age gives him a
solid and heavy globose shell; and next, that he too, while young
and tender, and liable therefore to be bored through by whelks and
such murderous univalves, does actually possess the same briar-
prickles, which his thinner cousins keep throughout life.
Nevertheless, prickles, in all three species, are, as far as we can
see, useless in Torbay, where no wolf-fish (Anarrhichas lupus) or