394 MOLLUSCA. 



greatly elongated. There is much incertitude however with respect 

 to all these bodies(l). 



As to the well known living testaceous Acephala, Linnaeus 

 had united in the genus 



OsTREAj Lin., 



All those which have but a small ligament at the hinge, inserted 

 into a little depression on each side, and without teeth or projecting 

 plates. 



OsTREA, Brug. 



The true Oysters have the ligament as just described, and irregu- 

 lar inequivalve and lamellated shells. They adhere to rocks, piles, 

 and even to each other, by their most convex valve. 



The animal Peloris, Poli, 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 hingej but there is no vestige of a foot. 



O. edulis, L. The common oyster is well known to everyone. 

 Its fecundity is as astonishing as its flavour is delicious. Among 

 the neighbouring species we may observe, 



O. cristata, Poli, II, xx, or the little Mediterranean oyster. 

 Among the foreign species we have, 



O, parasitica, L.; Chemn., VIII, Ixxiv, 681. Round and flatj 

 it adheres to the roots of such mangroves and other trees of the 

 torrid zone, as the salt-water can reach. 



O. folium, L.; lb., Ixxi, 662, 666. Ovalj the margin plicated in 

 zig-zag; it attaches itself by the indentations in the back of its 

 convex valve to the branches of the Gorgoniae and other Litho- 

 phytes(2). 

 M. de Lamarck separates by the name of 



(1) The observations of M. Deshayes and Audouin even lead us to believe that, 

 in apart of these shells, there were two muscular impressions. 



(2) The various species of Oysters, on account of their irregularity, are not 

 easily distinguished: to this genus are referred the Ost. orbicularis; 0. fornicata,- 

 0. sinensis; 0. PorshahUi; 0. rostruta; 0. virginicu; 0. co7-nucopix; 0. 

 senegalensis; 0. stellata;0. ovalis; 0. papyracea, and the Mytilus crista-galli; 

 M. hyotis; M. frons, Gmel., and those figured by Brugiere in the Encyc. Me- 

 thod., pi. 179, 188. 



It is almost certain, however, that several of these pretended species are mere 

 varieties. 



The Ost. semi-aurita, Gualt., 84, H, is a young AviculaMrundo. 



