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Honjo to Know American Seashells 71
auctions. If Anachis avara is swarming over an oyster bed, no one takes
particular note, but the mere mention of the Destructive Oyster Drill, Uro-
salpinx 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 reahzed 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 laiitellosa) . 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 dif-
ferences in the color patterns of the animals shown on plate 8.
Marine mollusks are exceedingly responsive to varying ecological con-
ditions. 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 ques-
tion, 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 morpho-
logical, 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 con-
tinuous 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