SHELLS. 



55 



bishop's miter, and are found in the Philippine Islands. If an 

 enemy approaches, their occupants throw out a purple fluid and 

 escape under cover of the stained water. 



Notice in the miter shell how the color spots correspond to 

 the whorls, in the scallops how the shades and bands follow the 

 lines of growth. Have you ever thought why this is so ? The 

 mantle which builds the shell has spots or bands of color scat- 

 tered through it, and as it works, the impressions of these same 

 pigment spots are left on the shell. If the pigment cells of the 

 mantle be yellow, red, or violet, these colors will be left on the 

 shell and preserved forever. 



Another marvelous accomplishment of the mantle is the orna- 

 mentation of shells with prongs, flutings, etc. We have a good 

 example of this in the lovely Murex shells. The mantle some- 

 times works without cessation until the shell is finished, then 

 turns up, forming the lip (the edge of the aperture). Often it 

 works for a time, turns up, forming a frill or row of points, and 

 rests. Then it begins its labors anew, building an addition and 

 ornamenting it in like manner. Sometimes the mantle turns up 

 at the end in a number of fingerlike radiations, as in the Ptero- 

 cera lanibis and curious pelican's foot. 



The cowries form an immense group, some species of which 

 inhabit almost every shore. They are called porcelain shells, on 



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Miirex rarnoRus. 



account of their glossy, smooth texture. The little white cowries 

 are used in some parts of Africa for money and to make girdles 

 for the high chiefs. A stripe of a different shade from the 

 body of the shell runs along the back, showing where the edges 

 of the mantle met. In life it entirely covers the outside of 

 the shell, \ 



The helmet shells of warm seas are used for making exquisite 

 cameos, the best being cut at Rome. The raised figure is chis- 



