PEDUM. 



Brug.—Encyci. Method, t. 178. f. 1—4. 



TESTA elongato-securiformis, compressa^ inaequi- 

 valvis, subauriculata, adhaerens ; umbonihus pau- 

 lum distantibiis. Valva inferior prope cardinem 

 profunde sinuata, lateribus reflexis; discus del- 

 toideus cardinis fossiila obliqua elongata liga- 

 mentum inserviente. Valva superior lateribus 

 iiicrassatis^ discus deltoideus cardinis minus expan- 

 sus^ cicatricula elongata obliqua ligamentum ge- 

 rente. Impressio muscularis unica^ suborbicularis. 



Very properly separated from Ostrea by Bruguiere.^ and 

 adopted by succeeding writers; it differs from the true 

 Ostrea in the mode of attachment, adhering by a (probably 

 fibrous and horny) substance which passes through the 

 sinus in the lower valve, whereas Ostrea is attached by the 

 outside of the shell itself. The shell of Pedum is compressed, 

 inequiyalve, subauriculate, rather longer than it is wide, 

 and wider at the base than at the hinge ; the wnhones are 

 somewhat distant. The sides of the lower valve are turned 

 upward in all the specimens we have had the opportunity 

 of examining, and there is a deep sinus, for the passage of 

 the substance by which the animal attaches itself, near the 

 hinge on the left hand side ; a triangular disk with an ob- 

 lique elongated central furrow bears the hinge ligament 

 in this valve. The sides of the upper valve are thickened, 

 the triangular disk in the hinge of this valve is smaller than 

 that in the lower valve, and it has an elongated oblique 

 cicatrice opposite to the furrow of the other valve to which 

 the hinge ligament is attached. The principal portion of 

 the ligament is attached to the central furrow in the tri- 



