ch. ix THE COLOURS AND PIGMENTS OF MOLLUSCA 185 
dent with the most gorgeous colours. This giant 
clam occurs freely among the corals of the Australian 
Barrier Reef, and during life the valves gape widely, 
disclosing the frilled mantle-folds which give the 
species its popular name. These are often coloured 
with shades of blue varying from “ palest turquoise 
to the richest ultramarine,” or are green variegated 
with spots and markings of black. Sometimes the 
ground colour is purple or rich brown spotted and 
streaked with bright blue or green. The shell in 
this clam is a pale yellow, and the organisms are 
exceedingly conspicuous on the reefs. In many 
Molluscs the pigments of the mantle are confined to 
special spots, as in the case of the simple “ eyes ” 
of many Lamellibranchs, but cases of uniformly 
diffused colour are far from uncommon. The 
delicate pink colouring of the fringed mantle-folds of 
Lima is familiar to all those who have done coast 
dredging. In Patella vulgata, the common limpet, 
the dorsal body wall is of a deep blue-black colour, 
while in the little tortoise-shell limpet (Acmcea 
testudinalis), common on Scotch coasts, the same 
region is a delicate blue-green. In the shell-less 
Gasteropods, such as the sea-slugs ( Doris , etc.) and 
the terrestrial slugs Limax, etc., the whole of the body 
wall is usually coloured, often with bright pigments, 
but this is much less inexplicable than the occurrence 
in the mantle of shelled forms of bright pigments 
having no obvious relation to the pigments of the 
shell. 
As to the colours of the Cephalopoda there is 
little need either for description or eulogy ; most 
people must have seen and admired the lovely 
