158 THE HALL OF SHELLS. 
have raised figures of yellow on a_ pink 
oround. 
“As has been seen, the shells used for these 
jewels and called cameo shells are generally 
the large Cassides. The carving of the cameos 
is a fine art, carried to an exquisite perfection 
by the Roman cameo cutters.” 
“ What gives the different colors to shells?” 
asked Tom. 
“That is another of the mysteries in which 
Nature has been chary of her confidences,” an- 
swered Miss Bremely. “It seems to be in 
some way the result of a secreting work done 
by the border of the mantle. Light also 1s 
their painter. We observe that shells near the 
shore are richer and brighter in colorimg than 
those which are shut out from the sunlight in 
deep ocean beds. Tropic seas yield us the 
most brilliantly colored shells, as tropic groves 
produce birds of gayest plumage. 
“George W. Tryon tells us in his Conchol- 
ogy that ‘bivalves which habitually he upon 
one side have the upper valve colored and 
pictured, while the under valve is white and 
colorless. He also quotes authorities who 
seem to have discovered in certain cases an 
adaptation in the color of shells to the color of 
objects upon which they rest. 
