BIVALVES. 65 
principle of beauty holds a considerable place in their 
composition, and is still more predominant than in 
animals. Why, for instance, are the shells of the 
genus Cardium, or Cockle, frequently of a dark 
brown colour, varied with white hollow elevated ribs? 
Why are those of the Tellina, or Tellen, so remarkable 
for their beautiful radiations; and why are so many 
species of the Venus unrivalled in the brilliant tint- 
ings and lustre of their shells; the rich purple (Venus 
mercenaria), or Money-Venus, especially, which is 
used by the Indians of North America to form the 
purple and white beads of their wampum, or treaty 
belts? The purpose, so far as we can see, of animal 
nutrition might have been carried on as well under 
the sober coating of the garden snail. Or, if this 
could not be in every species, for reasons inexplicable 
to us, why break into such a variety of colours? It 
is not an effect of age, or of any declension in the 
vigour of the subject, for the young and active are 
generally most distinguished for the prilliancy of 
their tints. This property in the shell is evidently 
independent of the inhabitant ; it is solely calculated 
for beauty, intended for display. In none of the 
numerous family of Testacea is this property more 
remarkable than in the hundred and fifteen species of 
this elegant genus, most of which are celebrated for 
the smoothness and brilliancy, as well as the rich 
F 
