ORDER TESTACEA. 93 
OsTREA, Lin., 
All those which have but a small ligament at the hinge, in- 
serted into a little depression on each side, and without teeth 
or projecting plates. 
OsTREA, Brug. 
The true oysters have the ligament as above described, and 
iregular inequivalve, and lamellated shells. They adhere to 
rocks, piles, and even to each other, by their most convex 
valve. 
The animal (PELOoRIS, Pol) is one of the most simple of 
all the bivalves, possessing nothing remarkable but a double 
fringe round the mantle, the lobes of which are only united 
above the head, near the hinge; but there is no vestige of a 
foot. 
Every one is acquainted with the common oyster (Ostrea 
edulis, L.), which is gathered upon the rocks, and reared in 
depots, to be ready when wanting. Its fecundity is as 
astonishing as its flavour is agreeable. 
Among the neighbouring species we should notice 
The little Mediterranean oyster. (Ostrea cristata, Poli. 
IT xx.) 
Among the foreign species we should remark 
The Parasite oyster (Ostrea parasitica, L.), Chemn. VIII. 
Ixxiv. 681, 
Round and flat, which fixes itself on the roots of the man- 
groves and other trees, which the salt water can reach. 
The leaf oyster (Ostrea folium, L.) Ibid. lxxi. 662—666. 
Oval, with the margins folded in zig-zags, which attaches 
itself by the indentations of its convex valve to the branches 
of the Gorgoniz and the other Lithophytes. 
M. de Lamarck separates by the name of 
