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 



