PECTEN. 59 



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

 sharper, and the surface resembles shagreen. 



3. P. opercula'ris"*, Limie. 



Ostrea opercularis, Linn. Syst. Nat. p. 1 147. P. opercular is, F. & H. ii. 

 p. 299, pi. L. f. 3 ; li. f. 5, 6 ; liii. 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 fila- 

 ments : ocelli 35-40, nearly globose, having pearl- coloured 

 pupils within black circles : foot small, subcylindrical, deeply 

 cloven or furrowed, 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 : smlpture, 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 each 

 side from about three-fourths of the distance from the front 

 margin ; slope below the byssal sinus strongly toothed or ser- 

 rate : beaks prominent : ears nearly equal, sculptured by ribs 

 which radiate from the beak; the ears of the lower valve 

 slightly project beyond and overlap those of the upper valve ; 

 byssal notch deep : hinge-line straight : cartilage rather large : 

 ligament narrow and slight: hinge-plate somewhat broad, 

 minutely striate across ; transverse rib strong and raised on 

 each side of the cartilage-pit : inside fluted or grooved, so as 

 to correspond with the folds of the outside ribs ; each shoulder 

 under the ears is furnished with a thick ledge, which rests on 

 that in the opposite valve, thus giving additional support to the 



* Like a cover or pot-lid. 



