OSTREA. 



The Ostreae, including- Gryphasa, may be conveniently 

 divided into three sections, as follows : 



§ 1. Testa margine simplice, vel subundato. To this section belongs the 

 common Oyster and such other species as have no distinct folds around the 

 ■edges. 



§ 2. Testa margine plicato. To this section belong the Cockscomb 

 Oyster, (Ostrea Crista galli, Lam.^ and other species whose edges are strongly 

 and sharply plicated. Linne has placed several of them among his Mytili. 



^ 3. Testa unihone majoris valvce involuto ; aiid to this section belong 

 the GryphiSCB and Podopsides of Lam. 



The OstrejB, as every body well knows, are marine ; 

 in their young state they are attached to rocks and other 

 submarine bodies, frequently to each other ; and it is pro- 

 bable that they remain so for a considerable part of their 

 life, though under certain circumstances they seem also to 

 have the power of dislodging themselves, without being af- 

 terwards subjected to inconvenience. The outer part of 

 the shells is of an imbricated and foliaceous substance, 

 composed of minute perpendicular fibres, different how- 

 ever from that part of the inside to which the animal is 

 for the most part confined, which is of a much more com- 

 pact nature^ and if composed also of aggregated fibres, 

 they are not placed in the same position, with respect to 

 the animal, as those of the outer part. 



There is a circumstance mentioned by Lamarck (but 

 we believe that Lamarck is not the first who made the 

 observation, though if he be not, he has implicitly adopted 

 it from some other conchologist, without giving the author's 

 name) which we should be very glad to pass over in si- 

 lence ; for, either we are so extremely dull as not to com- 

 prehend it, or the circumstance, as related, is itself so 

 exceedingly absurd, that we could have wished, for the 

 credit of science, that it had never disgraced the pages of 

 any books on Natural History : that Lamarck may not be 

 misunderstood, we must quote his own words, without at- 

 tempting to translate them : " Une particularite fort re- 

 marquable, qui appartient a un grand nombre d'especes 

 de ce genre, et qui paroit ne leur dire commune qu'avec 

 ies spondyles, c'est qu'a mesure que Fanimal grandit et 

 vieillit, il est force de se deplacer dans sa coquille et de 

 s'eloigner graduellement de la base de sa valve inferieure ; 

 or en se depla^ant, il deplace en meme temps la valve 

 superieure de sa coquille, ainsi que le ligament des valves ; 



