] 74 Conchology. 



porcelain and other shells. The form of the shell is also changed 

 in a remarkable manner, a great quantity of testaceous matter be- 

 ing deposited on the surface of the opening, which then assumes 

 a considerable thickness. The turns of the spire are incrusted, 

 and sometimes disappear on the outside of the shell; and wrinkles, 

 furrows, and even tubercles, which exist on the surface of some 

 species, are also formed. The surface of the Cyprceapediculusex-' 

 hibits circular striae which did not originally exist, which owe their 

 formation to this cause. In other species, the surface is marked 

 with projecting points or tubercles, which are prodiaced in the 

 same manner as the circular striae of the former, and which also 

 depend on the structure of the membranaceous wings of the ani- 

 mal and the testaceous substance which is secreted and deposited 

 from their surface. Thus, it appears that porcelain shells, and 

 those of some other species, are formed at two distinct periods. 

 It is during the second period of the process that the color of the 

 complete shell is formed. In farther illustration of this point, of 

 the formation of shells of this description at two different periods, 

 one or two examples may be given of the difference which takes 

 place, when the last layer formed is removed. In the Cyprcea ex- 

 anthema, the shell is ferrugineous, with whitish, round spots and 

 eyes, but when the outer coat is worn off, it becomes barred or 

 tessalated with brown or blue. The Cyprcea arabica, as its name 

 imports, exhibits characters on its surface, having some resem- 

 blance to Arabic letters. The ground on which these characters, 

 which are of a brown color are placed, is whitish or bluish; yet 

 when the outer coat is worn down, the shell is sometimes mark- 

 ed with blue or brown bands, or pale with darker angular spots and 

 lines; brown, mixed with violet, or reddish blue. 



But besides the causes which have been mentioned concerning 

 the production and variety of the colors of shells, arising from the 

 difference of structures in the organs which secrete the coloring 

 matter, and the changes to which these organs are subjected in 

 the growth of the animal, the effects of light and heat, altogether 

 independent of the animal itself, are probably very considerable. 

 Two individuals of the same species, the one from the Mediter- 

 ranean or European seas, and the other from the tropical regions, 

 exhibit very different shades of colors. The colors of the inhab- 

 itants of the torrid zone are always more bright and vivid than those 

 of the natives of more temperate climates. The two shells, although 

 similar in form, size and other characters are uniformly different 

 in *he intensity of their colors. These differences, which have led 

 conchologists to increase the number of species, obviously depend 

 on the action of the climate, and particularly of light, on nourish- 



