84 MOLLUSCA. 



SPHJERULITES Lameth., 



Where the valves are roughened hy irregularly raised plates. It 

 is also thought we may add the 



CALCEOLA, 



One valve of which is conical but free, and the other flat and even, 

 somewhat concave, so that they remind us of a shoe ; and even the 



HIFPURITES, 



Where one valve is conical or cylindrical with two obtuse, longi- 

 tudinal ridges on the inside ; the base even appears to be divided into 

 several cells by transverse septa*; the other valve fits like a cover. 

 The 



BATOLITHES, Montf. 334, 



Are cylindrical and straight Hippurites ; they are frequently found 

 greatly elongated. There is much incertitude, however, with respect 

 to all these bodies f . 



As to the well known living testaceous Acephala, Linnaeus had 

 united in the genus 



OSTREA, 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 hinge ; but there is no vestige of a foot. 



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

 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 flat ; 

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

 torrid zone, as the salt-water can reach. 



* See Deshayes, Ann. des Sc. Nat., June, 1825 ; and Ch. Desmoulins, loc. cit. 

 Several Hippurites have been described by La Peyrouse under the improper name of 

 (...Ihoceratiles. The Cornucopia of Thompson, Journ de Phys. an X, pi. ii, is also 

 one of them. 



f The observations of M. Deshayes and Audouin even lead us to believe that, in a 

 part of these shells, there were two muscular impressions. 



