1 70 OYSTERS, AND ALL ABOUT THEM. 



that it does not now exist anywhere on the Swedish coast, 

 although it is common there in a fossil state. This species 

 is not unlike the variety niveus of P. varius in shape and the 

 number of ribs ; but the shell is more solid, the ribs 

 sharper, and the surface resembles shagreen. 



3. P. OPERCULARIS, Linne. 



Ostrea opercularis, Linn. Syst. Nat., p. 1147. P. opercularis, 

 F. and H. 2, p. 299, pi. 50. f . 3 ; 51. f. 5, 6 ; 53, f. 7. 



BODY thick, variegated with pink, cream-colour, 

 fawn, orange, or brown, and mottled with flake-white 

 meandering lines, spots, and blotches : mantle thin, except 

 at the fleshy margins : cirri conical, white, of unequal 

 length and irregularly disposed in two or three rows, the 

 outer one of which has the longest filaments : ocelli 35-40, 

 nearly globose, having pearl-coloured pupils within black 

 circles : foot small, subcylindrical, deeply cloven or fur- 

 rowed, and scoop-shaped at its extremity, of a yellowish- 

 white colour. 



SHELL circular and equilateral, except at the back 

 (where the periphery is interrupted by the beak and ears), 

 rather thin, scarcely glossy : Sculpture, about 20 rounded 

 ribs, which are of equal size and somewhat broader than 

 the interstices ; the surface is more or less covered with 

 extremely fine and wave-like transverse plates, which often 

 form numerous rows of short prickles, especially along the 

 ribs and on their crests, making the shell feel rough as 

 shagreen : colour red, pink, orange, yellow, purple, brown, 

 or of intermediate shades, often streaked or marked with 

 blotches or spots, and sometimes (but rarely) milk-white : 

 margins rounded in front and at the sides, notched or 

 indented by the ribs, sloping gradually to the beak on 



