Conchology. 5 



Cowry (Gyprcea 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 lamince, as they are termed, closely packed to- 

 gether. The thinner these laminaa 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 rainbow, 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 



