370 



THE GEOLOGIST. 



transporte sur le cote aiiterieur de I'animal, u'est plas en antagonisme 

 direct avec le ligament, et nous comprenons tres-bien les motifs de 

 I'hesitation de M. Woodward a ce sujet. L'absence d'un muscle du 

 cote posterieur de la coquille laisse a deviner I'usage des deux aretes 

 saillantes dans I'mterieur du meme cote, et celui des oscules de la 

 valve superieure qui leur correspondent. J'accueillerais volontiers 

 I'idee de M. Bayle, qui suppose aux oscules la fonction de laisser 

 penetrer I'eau dans la cavite du manteau, et ils correspondraient aux 

 siphons de I'animal ; c'est une vue theorique qui peut paraitre plau- 

 sible, mais quin'a rien de proiive."* 



It must be regretted that M. Deshayes, whose notoriety as a con- 

 chologist was increased at the time by the circumstance of being 

 President of the Geological Society of France, should have enunciated 

 views which would be inexcusable in the veriest tyro in malacology. 

 Their publication was the more surprising to me, because he had only 

 just before examined my materials very fully and deliberately, and 

 expressed his entire approval of my conclusions. If the author of 

 the ' Mollusques Algeriennes ' would have taken the trouble to read 

 my account of the Tridaana,^ or, better still, if he had examined for 

 himself one of the specimens brought home by Quoy and other cele- 

 brated voyagers, who have enriched the public museums of France, 

 he would not have attributed to that bivalve a structure altogether 

 incompatible with lamellibranchiate organization. 



The readers of the ' Geologist ' will pardon us for reminding them 

 of such an elementary fact as that the bivalve shells like Chama 

 are closed by two shell-muscles {adductors), one situated over or 

 heliind the mouth of the animal, the other in front of the posterior 

 portion of the digestive canal. The whole body of the animal lies 

 between them. The posterior adductor is developed first, and is in- 

 variably present. The anterior is usually smaller, and is wanting in 

 the " monomyary " families, OstreidcB, FectinidcE, Anorniadcs, Tridac- 

 nidcB, and most of the AviculidcB. In Midleria it is always lost by 

 the breaking away of the front of the valves, and sometimes it is 

 worn away in Clavagella. In Pliolas the expansion and reflection of 

 the front margin gives the anterior adductor a position which converts 

 it into a cardinal muscle. In Tridacna the single sliell-muscle is 

 placed just as in the oyster; that which M. Deshayes has mistaken 

 for a second adductor, is the pedal muscle, which is conspicuous in 

 all bivalves spinning a byssus, or having a powerful foot. 



Tlie posterior adductor of the ITippurite is situated exactly as in 

 tlie Iladiolite, but the supporting process projects verticall^y instead 

 of expanding horizontally, and passes down into, but does not nearly 

 fill, tlie deep pit between the hinge-teeth and the projecting ridge 

 which we have compared to the muscular plate of Cuculla'a and 

 otlier bivalves. J Tlie position of this muscle is well represented by 

 Goldfuss (at 6''), in his small figure of tlie mould of H. Lapeirousii. 



* WnW. Soc. Gcol. France, seance du 21 mai 1855 (puhlislicd jMavcli, 1856.) 



t Ann. Nat. Hist., Feb, 1855, p. 100, and Supplement to ' Manual of Mollusca,' p. 469. 



} Especially Cardilia, Mejalodon, Pachijrisma, Liccras, and Ca^rotina. 



