BIVALVE MOLLUSCA<g 401. 
Pectens.are very variable, but always elegant in form; the colours are 
frequently lively and brilliant. In PLate XVIII. some of the most 
striking forms are represented, as in Fig. L., the Ducal Mantle (Pecten 
patlium), an inhabitant of the Indian Ocean, remarkable for its 
elegant form, its twelve radiating stripes, diverging towards the cir- 
cumference, the horizontal furrows of its salient scales, and the 
striking distribution of its white spots upon a bed of red and brown’ 
marble; Fig. II., the Purple Pecten; Fig. III., the Coral Pecten ; 
Fig. IV., the Tiger Pecten; Fig. V., the Foliaceous Pecten; and 
Fig. VI., the Northern Pecten. 
The animal which inhabits the shells belonging to this genus has 
Fig. 174.—Pecten pseudamussium (Chenu). Fig. 175.—Pecten glaber (Linnzus.) 
the general form of the oyster, differing however from it in a remark- 
able manner. The edges of the mantle are furnished with multiplied 
fringes of simple tentacles, between which we find other tentacular 
appendages a little thicker, each terminating In a sort of small pearl, 
vividly coloured, which has been taken for an eye, and to which is 
attached a nervous thread. Another difference is that the branchiz, in 
place of being connected to each other and the mantle lobes forming 
as in Ostrea a complete branchial chamber, here are crescent-shaped, - 
and are quite unconnected posteriorly, and have excurrent canals. 
The mouth is provided with foliaceous lips, and a foot is present; 
somewhat finger-like, grooved, and byssiferous when young. 
While the oyster shell is completely fixed to its bed, the Pecten is, 
on the contrary, perfectly free, and shifts from place to place, moving 
in the water even with a certain amount of agility ; by smartly closing 
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