16 INTEODUCTION TO CONCHOLOGY. 



that of form, are so peculiar, that the shell-collector should 

 obtain specimens at different periods of their growth. 



Eirst then, and as presenting the earliest attempt made 

 by a young Cowry towards constructing a dwelling, appears 

 a simple convolution of shell around the columella axis, in 

 the form of a long drawn-out Bulla, the columella being 

 smooth, the outer lip thin, and the colour usually diffused 

 in wavy bands. 



A second epoch of growth succeeds ; the shell becomes 

 more solid, the lip and columella begin to thicken, and 

 present gradual indications of teeth, which develope more 

 and more, and the surface is overlaid with a strong coat of 

 livid colouring matter diffused in obscure bands or waves. 

 Another process ensues ; for the calcifying energies of the 

 mantle, which extending in two unequal lobes from either 

 side of the shelFs aperture, have been hitherto chiefly 

 encrusted upon the back of the dorsal surface, during the 

 second epoch of growth, are now more particularly directed 

 to the base and sides. The teeth are strengthened, the sides 

 become thickened with a rich coating of enamel, and the 

 beauty of the superb arch is rendered perfect by lines or 

 waves, or net-work, of various hues and patterns. 



In most species three separate phases of colour pertain to 

 different periods of growth. In the C. Mauritiana , for 



