37G 
THE GEOLOGIST. 
traiisporte sur le cote anterieur de I'animal, n'est plus en antagoiiisme 
direct avec le ligament, et nous compreuons tres-bien les motifs de 
I'hesitation de M. AVoodward 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'interieur 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 tbeorique qui peut paraitre plau- 
sible, mais qui n'a rien de prouve."* 
It must be regretted that M. Deshayes, whose notoriety as a con- 
chologist was increased at the time by the circuinstance of being 
President of the Geological Society of Prance, should have enunciated 
views which would be inexcusable in the veriest tyro in malacologv. 
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 Tridacna,-\ 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, Ostreidw, Pectinidce, AnomiadcB, Tridac- 
nidcB, and most of the Aviculidcd. In Mulleria it is always lost by 
the breaking away of the front of the valves, and sometimes it is 
worn away in Clavagella. In Fholas 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 shell-muscle is 
plnced just as in the oyster; that which M. Deshayes has mistaken 
fur a second adductor, is the pedal muscle, which is conspicuous iu 
all bivalves spinning a byssus, or having a powerful foot. 
T!ie posterior adductor of the Hippurite is situated exactly as in 
the Kadiolite, but the supporting process projects vertically instead 
of expanding horizontally, and passes down into, but docs not nearly 
fill, the deep pit between the hinge-teeth and the projecting ridge {m), 
which we have compared to the muscular plate of Ciicullcea and 
other bivalves.;]: The position of this muscle is well represented by 
GoldfusB (at c), in his small figure of the mould of H. Lapeirousii. 
* Bull. Soc. Geol. France, seance du 21 niai 1855 (published March, 1856.) 
t Ann. Nat. Hist., Feb. 1855, p. 100, and Supplement to ' Manual of iSIollusca/ p. 469. 
:|: Especially Cardilia, Megalodon, Pachi/risina, Diceras, and Caprotina. 
