224 WEST COAST SHELLS 



But the iridescent colors of mother-of-pearl are 

 due to quite another cause. There is no dye-stuif 

 about it; nothing but extremely thin layers of shell 

 overlapj)ing one another like the shingles of a micro- 

 scopic roof. But these projecting shingle-ends so 

 shiver the beams of sunshine into their primar}^ colors 

 that the white light is sent off in its parts, red, blue, 

 green and other tints, just as we see them in the 

 rainbow. And therefore as we turn the shell so as to 

 bring its surface to the eye at a new angle we get 

 changes of color, because we get a diiferent reflection. 

 Many sea-shells are nearly white, some have distinct 

 but solid colors, but the shells described in this chap- 

 ter, together with the pearl oysters and a few others 

 are the true pearl-makers of the world. 



Many of the shells of these pearl-makers take the 

 form of turbans or tops, and each little creature has 

 a special front door which he closes whenever he par- 

 ticularly desires to be alone. The apertures of nearly 

 all of these shells are nearly circular, and are wholly 

 without canals; which is a pretty good proof that the 

 inmates should be classed with the vegetarians. The 

 opercula of a few of our species are solid and shelly, 

 while in most species they are more like a scale of 

 horn. We begin our descriptions with those of the 

 first kind, and it ha])pens that our very first shell is 

 an exception to the general law, and has a perfectly 

 white interior, without a rainbow of any kind. 



Fhasianella compta,, Gld., the Pheasant- 

 shell, Figure 217, may sometimes be found 

 alive on sea-grass, though dead shells are 

 Fig. 217 more common. When alive, there is a dull 



