GROWTH OF SHELLS. 157 
of a chamber which the animal has outgrown 
and vacated, he does not again enter the ‘halls 
of the past,’ but deliberately shuts out the past 
and its injuries alike, by building a shelly wall 
or partition entirely across that part of the 
shell, 
“The different depositions or layers are 
sometimes shown when the edges of a shell be- 
come broken. They are also seen in the cameo 
shells, in which the laminations are of different 
colors, You will see what I mean by this,” 
she said, unfastening from her collar a brooch 
of shell cameo. Holding it to the light she 
displayed the delicate translucence of the 
orange ground over which figures were carved 
from the next layer in white relief. “This 
shows the strata of the shell,” she said, “and 
also how the colors have been turned to account 
in carving the jewel. The shell from which this 
was cut was known as Cass¢s cornuta ; its habi- 
tat was the Indian Ocean. 
“ All cameos are not colored like this. Some 
are a pale salmon on an orange ground. Such 
are cut from the Cassis rufa. Others, from C. 
Madagascariensis and C. tuberosa, have white 
figures on dark claret-colored ground. Some 
are cut from the Strombus gigas, which is the 
pinky queen’s couch of the West Indies. These 
