148 OYSTERS, AND ALT, ABOUT THEM. 



manner; lines of growth irregular: colour yellowish- white, 

 with frequently reddish-brown, but not continuous streaks 

 or spots : margins thin, scalloped or notched by the ribs, 

 nearly straight behind : beak small, rather prominent, very 

 seldom reaching to the hind margin, and never overlapping 

 it: cartilage short and narrow, fixed in a cavity beneath the 

 hinge: hinge-line slightly curved: hinge-plate thick but. 

 narrow : orifice rather large, much broader below than 

 above ; outer edge not reflected : inside bluish-green, 

 highly iridescent, furnished in the lower valve with a ledge 

 to receive the cartilage : muscular scar large, showing in the 

 upper valve the impression of two inner portions of the 

 muscle of a roundish-oval shape and often confluent, the 

 larger one of which is placed in the middle, and the smaller 

 one a little below it on the left hand side ; in the lower 

 valve there is only one impression, placed as in the last 

 species : plug pear-shaped, thin, and coarsely striate 

 lengthwise. Length 1*3, breadth i'45. 



Var. striata. Shell sometimes nearly -convex, covered 

 with numerous and fine longitudinal striae, which often rise 

 into minute scales, becoming prickly and occasionally 

 decussated by the transverse lines of growth ; coloured 

 rays more distinct and somewhat wavy. A. striata, Loven, 

 Ind. Moll. Scand., p. 29. F. & H., 2. p. 336, pi. 55, f. i. 

 6, and pi. 53, f. 6. 



HABITAT: 10-86 fathoms, on hard ground and shell- 

 banks everywhere, usually concealed in the hollows of old 

 bivalves. It is, however, not so common as the last 

 species, although equally diffused ; and they are found 

 together. The variety occurs in Shetland and on the west 

 coast of Scotland. A. patelliformis is a tertiary fossil of the 

 Clyde beds, and of the Red and Coralline Crag, as well as 



