Certain species of _Strombus_ (_mauritianus_ L., _luhuanus_ L.) show a remarkable similarity in the shape of the shell to that of _Conus_, so much so, that a tiro would be sure to mistake them, at first sight, for Cones. In the case of _S. luhuanus_ at least, this similarity is increased by the possession of a remarkably stout brown epidermis. Now _Conus_ is a flesh-eating genus, armed with very powerful teeth which are capable of inflicting even on man a poisonous and sometimes fatal wound (see p. 66). _Strombus_, on the other hand, is probably frugivorous, and is furnished with weak and inoffensive teeth. It is possible that this resemblance is a case of ‘mimicry.’ It is quite conceivable that powerful fishes which would swallow a _Strombus_ whole and not suffer for it, might acquire a distaste for a Cone, which was capable of lacerating their insides after being swallowed. And therefore the more like a Cone the _Strombus_ became, the better chance it would have of being passed over as an ineligible article of food. _Protective coloration_ is not uncommon among the Mollusca. _Littorina obtusata_ is habitually found, on our own coasts, on _Fucus vesiculosus_, the air-bladders of which it closely resembles in colour and shape. _Littorina pagodus_, a large and showy species, resembles so closely the spongy crumbling rocks of Timor, on which it lives, that it can hardly be discerned a pace off. _Helcion pellucidum_, the common British ‘blue limpet,’ lives, when young, almost exclusively on the iridescent leaves of the great Laminariae, with the hues of which its own conspicuous blue lines harmonise exactly. In mature life, when the _Helcion_ invariably transfers its place of abode to the lower parts of the stalk and finally to the root of the Laminaria, which are quite destitute of iridescence, these blue lines disappear or become much less marked. The specimens of _Purpura lapillus_ which occur at Newquay in Cornwall are banded with rings of colour, especially with black and white, in a more varied and striking way than any other specimens that have ever occurred to my notice. I am inclined to refer this peculiarity to a tendency towards protective coloration, since the rocks on which the _Purpura_ occurs are often banded with veins of white and colour, and variegated to a very marked extent. _Ovula_ varies the colour of its shell from yellow to red, to match the colour of the _Gorgonia_ on which it lives. The same is the case with _Pedicularia_, which occurs on red and yellow coral.