121 



Lamarck observes that the different length of the 

 beak at the summit of the lower valve is accounted for, 

 by theanimal possessing the faculty of displacing the up- 

 per valve as it requires increase of room, and bringing it 

 more forward towards the margin, similar to the plan he 

 states to be adopted by the Ostreae, and only observa- 

 ble in these two genera. 



It however appears, from the very singular position 

 of the two teeth on the valves of this shell, that they 

 are so securely interlocked with each other, as to re- 

 quire considerable force to separate the valves, and 

 which cannot be effected without breaking a portion 

 of that part of the lower cavities, into which the teeth 

 of the upper valve are inserted. Lamarck's assertion, 

 therefore, that the animal of this genus, as well as that 

 of G. Ostrea, possesses the power of removing the up- 

 per valve as its growth increases, is pointed out by 

 Sowerby as quite impossible and hypothetical in ei- 

 ther genus. 



Spondylus gaedaropus 



Americanus 



arachnoides 



candidus 



Spondylus costatus 



variegatus 



longispina 



regius 



multilamellatus avicularis 



