Conchology. 5 
Cowry (Cyprea Tigris) is a shell of this descrip- 
tion. 
Granular, or, as they are sometimes called, 
Concretionary shells, are the most hard and com- 
pact; it is in these that the substance called nacre, 
or mother-of-pearl, is mostly found. One of the 
commonest examples is the oyster shell; if broken 
across it will be seen to consist of very thin plates, 
or lamine, as they are termed, closely packed to- 
gether. The thinner these laminze may be, the 
more lustrous and beautiful appears the lining of 
the shell; that shifting play of colours which we 
call iridescent, from iris, the raimbow, is_ then 
brightest and most noticeable. A very remarkable 
substance is this mother-of-pearl ; smooth, and 
shining, and delicately-tinted. Who would expect 
to find such a beautiful lining to the rugged, rough, 
dingy-looking oyster, or mussel shell? ‘Truly these 
mollusks, some of them, live in gorgeous palaces. 
And the most curious part of the matter is that 
from the fluids or juices of their own bodies, and 
from the chalky matter collected from the water, 
they are enabled to secrete or deposit such wonder- 
fully-constructed habitations, which after all are 
little more than chalk. Burn a heap of oyster 
shells, or any other testaceous coverings, and you 
