1 86 OYSTERS, AND ALL ABOUT THEM. 



margin are of different lengths, and arranged in three 

 irregular rows : ocelli of a greenish-blue or purplish hue, 

 forming two rows, and numbering from 30-35 ; those in 

 the front row are considerably larger than the rest, and 

 correspond with the ribs of the shell : foot snow-white, 

 short, grooved, with a spatulate extremity. 



SHELL nearly circular, except behind, where the pro- 

 jecting ears give a square outline, equilateral above and 

 nearly so beneath ; upper valve slightly raised in the 

 middle, and smaller than the lower valve, which is very 

 convex ; it is thick and solid, glossy in the umbonal 

 region, but elsewhere of a dull hue: sculpture, 15 or 16 

 ribs in each valve, which radiate from the beaks and are 

 strong, and nearly as broad as the interstices between 

 them ; the ribs and interstices are scored by a few parallel 

 striae, which are more numerous on the lower than the 

 upper valve ; the whole surface is covered with minute and 

 close-set thin concentric plates, which are imbricated or 

 overlap one another like roof tiles : colour reddish-brown 

 on the upper valve, with a yellow tint on the lower valve ; 

 both valves are sometimes beautifully mottled or marked 

 with bands, zigzag streaks, and spots of burnt umber or 

 bright yellow, suffused with a delicate pink hue ; occasion- 

 ally, but rarely, the colour is white, with an orange tint at 

 the beaks : margins semicircular in front, and sloping at 

 the distance of about one-fourth from the hinge-line, at an 

 angle of 30 degrees to the beaks ; byssal slope not notched 

 or serrate : beaks small and not prominent in full-grown 

 specimens : ears exactly equal on the upper valve, and 

 nearly so on the other valve, furnished with a few ribs or 

 striae which radiate from the beaks ; byssal notch closed in 

 the adult state : hinge-line straight, rather more than half 



