119 



P. Pusio. Lam. 55. F. p. 385.Turt.p. 215. t. 

 17.y. 2. OSTREAP. Lin. 1146.? D. p. 261. Ch. 

 f. 635,6. Knorr. 4. t. 12. /. 2. Oblong-oval, equi- 

 valve, with about forty rounded and nearly smooth 

 striae, which are usually alternately larger and smaller, 

 and very slightly muricated about the margin ; variable 

 in coloring, often brownish white with chocolate ziczac 

 bands, or saffron or crimson, the under valve generally 

 pure white, ...&. Torbay, in rocks. 



P. JSLANDICUS. Turt. B. p. 216. -F. p. 385. 

 List. t. 1057. /. 4. Ribs numerous, rough, unequal, 

 from seventy to one hundred, grouped in pairs or other- 

 wise, reddisb, the furrows reticulated. 3...3-L W. 

 Scotland, rare. 



TRIBE. OSTRACEA. 



Ligament internal or semi-internal; shell irregular 

 and of a foliated texture. 



GENUS, OSTREA. 



Fixed, inequivalve, irregular, with the beaks more or 

 less separated from each other and becoming unequal 

 by age ; hinge toothless, with a cavity which is 

 partly external and in the lower valve becomes elon- 

 gated ; ligament internal 



