VARIETIES OF OYSTERS. 177 



what glossy : sculpture, extremely fine and numerous im- 

 pressed striae, which radiate from the beak and gradually 

 diverge to the front and side margins ; these striae are not 

 visible to the naked eye, and under a strong magnifier they 

 appear regularly but slightly punctured, in consequence of 

 the intersection of equally minute and close set transverse 

 striae, which follow the line of growth ; the longitudinal 

 striae are sometimes irregularly waved or interrupted, and 

 are often forked : colour yellow, brown, or purple, and now 

 and then white, with variously disposed bands, streaks, 

 blotches, spots, and other markings of those hues : mar- 

 gins rounded in front, so as to form a semicircle, and 

 sloping from near the middle to the beaks, at an angle of 

 about 45 degrees ; the front margin is sometimes folded 

 inwards and strongly notched ; the upper part of the slope 

 belo\v the byssal sinus is finely toothed : beaks very promi- 

 nent, and considerably raised : ears unequal ; those on the 

 left hand of the upper valve and right hand of the lower 

 valve are at least four times the size of the others ; all of 

 them have a few strong ribs which radiate from the beaks, 

 and they are also marked with coarse and numerous striae, 

 which cross the ribs obliquely ; the ears of the lower valve 

 project very little beyond those of the upper valve ; byssal 

 notch deep : hinge-line straight : cartilage small : ligament 

 very thin : hinge-plate narrow, microscopically striate 

 across ; transverse rib strong and considerably raised on 

 each side of the cartilage-pit : inside nacreous, finely and 

 closely striate lengthwise, and notched on the front mar- 

 gin ; within the larger ears are strong grooves, which 

 correspond with the outside ribs : muscular scars distinct, 

 especially in aged specimens. Length 0*9, breadth o'885. 

 Var. costata. Shell stronger than usual, and having 

 either five ribs and intermediate small ones, or else several 



