PLICATULA. OSTREA. 59 



" The genus is divided into sections, viz. ears 

 equal, ears unequal. You may find some common 

 species on our own shores, and you may procure 

 fossil species : they are numerous. 



^' Pllcatida is a genus taken from Spondylns. 

 Spondyliis gcBderopus, from the Mediterranean, 

 is a common shell in collections. 



" Podopsls is a fossil genus. 



" Ostracea. 



'^ The oysters and pectens differ so widely that 

 they do not even rank in the same family. 



" In the Ostracea are, 



Gryphma.., Ostrea. 



Ostrea The same. 



Vulsella. 



Placuna Anomia. 



Anomia The same — Antique lamp. 



'' There is but one recent species of the first 

 genus ; but many fossil. 



" The oyster is said to possess the most limited 

 faculties of all shelly tribes. Immovable upon the 

 rock or marine substance to which it is fastened, 

 it receives no other nourishment than what the 

 waves contribute, and indicates no other sign of 

 life than opening and closing the valve of the 

 shell. This genus still retains a great number of 

 species : one section has the margin of the shell 



