COLOUR OF SHELLS. 489 



are concealed within the bodies of their snails are always 

 white, as are also those which live in holes whence they never 

 issue. Another striking proof of the blanching effect of 

 darkness is furnished by some bivalve shells permanently 

 affixed by their lower valve, which is constantly white, 

 while the upper one may possibly be variegated with bright 

 colours. The Spondyli, and a number of Pectens, afford 

 examples of this contrast between their valves. Olivi has 

 further remarked, that the shells which are enveloped in 

 sponges, or other foreign bodies, or which burrow in sand, 

 or even which live in constantly shaded places, are much 

 paler than those which crawl about unprotected from the 

 light ; and even the exposed parts of the same shell are more 

 highly coloured than the parts which are shaded. 



On this point, Professor Edward Forbes has the following 

 remarks : — "A comparison of the Testacea and other animals 

 of the lowest zones with those of the higher, exhibits a very 

 great distinction in the hues of the species, those of the 

 depths being for the most part white or colourless, whilst 

 those of the higher regions, in a great number of instances, 

 exhibit brilliant combinations of colour. The results of an 

 inquiry into this subject are as follows : 



" The majority of shells of the lowest zone, are white or 

 transparent : if tinted, rose is the hue : a very few exhibit 

 markings of any other colour. In the seventh region, white 

 species are also very abundant, though by no means forming 

 a proportion so great as in the eighth, Brownish -red, the 

 prevalent hue of the Brachiopoda, also gives a character 

 of colour to the fauna of this zone : the Crustacea found in 

 it are red. In the sixth zone, the colours become brighter, 

 reds and yellows prevailing, generally, however, uniformly 

 colouring the shell. In the fifth region many species are 

 banded or clouded with various combinations of colours, and 

 the number of white species has greatly diminished. In 

 the fourth, purple hues are frequent, and contrasts of colour 

 common. In the third and second, green and blue tints are 

 met with, sometimes very vivid, but the gayest combinations 

 of colour are seen in the littoral zone, as well as the most 

 brilliant whites. 



" The animals of Testacea, and the Radiata of the higher 

 zones, are much more brilliantly coloured than those of the 

 lower, where they are usually white, whatever the hue of 

 the shell may be. Thus, the genus Trochus is an example 

 of a group of forms mostly presenting the most brilliant 

 hues, both of shell and animal ; but whilst the animals of 

 such species as inhabit the littoral zone, are gaily chequered 



