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Rh auctions. If Anachis avara is swarming over an oyster bed, no one takes particular note, but the mere mention of the Destructive Oyster Drill, Urosalpinx cinerea, brings the shell-fishery man to the scene to eliminate the pest.

The identification of one of the 6,000 species found in our waters is not always a simple task. True, by flipping through pages of illustrations we may spot the shell in question or at least a near relative. This method will sometimes bring us close enough so that reference to the text will reveal the correct identity. However, unless it is realized that many species differ only in seemingly slight characters and, conversely, that other species show wide variation in color or shape, misidentifications can result. How hopeless a task it would be to separate into species the various color varieties of the Common Coquina Shell (Donax variabilis) or the many shapes and sculptural varieties of the Western Dog Winkle (Thais lamellosa). Yet how many would not at first fail to notice the differences between the shell of McGinty’s Cyphoma and the Flamingo Tongue (Cyphoma gibbosa)? But look at the obvious differences in the color patterns of the animals shown on plate 8.

Marine mollusks are exceedingly responsive to varying ecological conditions. The presence of certain salts and minerals in the mud often dictates the degree to which certain colors are developed or to what extent spines are produced. In highly exposed areas, where surf waves pound against the shore, snail shells are usually devoid of delicate sculpture. These differences caused by environment are often difficult to distinguish from those which are genetic or naturally inherent characters of the species. So, too, there is often great genetic variation within a species, just as we have brunettes, blondes and redheads among humans. It is not an easy problem, even for the professional, to define the limits of a species, nor to say with authority that a certain specimen represents a “form” or is an example of a subspecies or even different species.

What is a species? Volumes have been written in answer to this question, and the subject is one of continuous investigation by many biologists working with all forms of animals and plants. Every population of mollusks is inherently different, and these differences, however minute, are morphological, physiological or genetic. One need only collect a common species in several localities along our coast and carefully examine them in order to reach this conclusion. It is this factor of geographical variation, together with timely isolation and selection, which has been largely responsible for the evolutionary production of species. The development of species is a continuous and very gradual process and, when we settle upon a reasonably homogeneous series of populations and label them as, say, Melongena corona, we are merely “snapping a candid camera shot” of a species living today, one whose picture looked quite different several million years ago during the Pliocene period. Within the geographical range of this species we find a