BIVALVES. 51 
quality is, I think, nowhere more conspicuous than 
in the forty-six different species which constitute 
the genus Mytilus. And in these what endless 
variety! Some are smooth, beautifully marbled, and 
variegated with delicate colours; others, elegantly 
radiated with white and purple; others, again, consist 
only of one colour, being either black or blue, green, 
brown, or yellow, coarsely ribbed, and grained with 
minute tubercles. 
Some of these exhibit internally a pearly appear- 
ance; others, when uncoated of a shaggy or bearded 
epidermis, and finely polished, display considerable 
brilliancy. The M. margariteferus, especially, is 
celebrated for its irridescent colours ; and is, besides, 
the Pearl-Muscle of the Indian seas; though beau- 
tiful and costly pearls are occasionally found in the 
Mya margaritifera, or Pearl-Gaper, as well as in Col- 
chester Oysters, and even under the armour of the 
Sea-hare. Nor is the inhabitant of the M. lithophagqus, 
which abounds in the Indian, European, and Mediter- 
ranean seas, where he burrows in rock and coral, less 
extraordinary for his silvery tinted shell, crossed 
with delicate oblique striz. He shines like phos- 
phorus in the dark, and hence the fishermen of the 
bay of Naples frequently place the animal in the sun, 
and afterwards rub their hands and faces with the 
moisture, till they render them luminous. 
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