l8o OYSTERS, AND ALL ABOUT THEM. 



it is at rest, the mantle forms a thick semicircular cushion, 

 striped across with yellow, brown, red, pink, and every 

 intermediate hue. 



SHELL somewhat resembling P. tigrinus in shape, but 

 rounder and much more depressed, rather thin and glossy: 

 sculpture minute longitudinal and transverse striae, which 

 are arranged as in the last species, but they are more, 

 regular and never forked ; they are deeply punctured at the 

 points of intersection ; sometimes there are also from 30-35 

 delicate ribs, which become scaly or prickly where they 

 are crossed by the transverse striae : colour yellow, orange, 

 brown, purple, pink, or occasionally white, usually diversi- 

 fied by streaks, rays, blotches, spots, diagonal lines, and 

 other markings of the above hues : margins rounded in 

 front, and forming an arc of two-thirds of a circle in con- 

 sequence of the lateral slopes towards the beaks commen- 

 cing higher up than in P. tigrinus ; byssal slope finely 

 toothed : beaks prominent, but not much raised : ears 

 unequal, those on the byssal side being about twice as 

 large as the other pair ; all of them have several fine ribs, 

 which radiate from the beaks and are crossed by coarse 

 flexuous striae ; the edges of the ears on the lower valve 

 project very slightly ; byssal sinus deep ; hinge-line straight, 

 finely notched or serrate at its edge : cartilage rather large : 

 ligament extremely slight : hinge-plate very narrow, micros- 

 copically striate across ; transverse rib slight, and not much 

 raised on each side of the cartilage-pit, which is propor- 

 tionally more open than in any of the foregoing species : 

 inside slightly nacreous, finely and closely striate length- 

 wise, or furrowed when the outside is ribbed : margin 

 sometimes notched or crenulated : muscular scars indis- 

 tinct, except in aged specimens. Length 0-575, breadth 



