536 



MEMOIRS OF THE CARNEGIE MUSEUM. 



terrupted, and more distinct in the anterior part of the shell. Even when best 

 developed, they do not constitute a prominent feature of the surface. Color of 

 epidermis dark olive-green to blackish. In young specimens it is more grayish 

 or brownish green towards the beaks; in older specimens it appears nearly black. 

 When slightly- worn, it is in places lighter, brownish olive, or greenish olive. In some 

 older specimens brownish tints appear towards the lower margin, and sometimes 

 a faint brownish concentric band is indicated. The general impression of the 

 color of the epidermis, however, is blackish green, not brown. No color-rays are 

 visible. 



Hinge-line gently curved. Ligamental sinus over the posterior third of the 

 laterals, in young specimens over the posterior half. Lateral teeth curved more 

 strongly in their posterior part in old shells, one in right, two in left valve, their 

 edges rough. Pseudocardinals directed obliquely forwards and downwards, 

 lamellar and compressed, but not very long. In the right valve there are two of 

 them, the posterior much larger than the anterior. In the left valve there is one 

 pseudocardinal, but quite often a smaller posterior one is present. All pseudo- 

 cardinals are rough, crenulated, or serrated. 



Cavity of. shell and beaks moderate. Nacre whitish, iridescent, in young 

 shells blueish or greenish silvery towards the edges. In older shells it becomes 

 more opaque white, and assumes generally a creamy or salmon hue in and near 

 the cavity. In a few specimens there is a very delicate pinkish tint all over the 

 nacre. 



T^terior adductor-scar rather deep, subelliptical; anterior retractor-scar 

 small, deep, isolated from the adductor-scar; anterior protractor-scar connected 

 with it. Posterior adductor-scar subtriangular, faintly impressed, posterior re- 

 tractor-scar forming an upper triangular process of it. Pallial line distinct. Dorsal 

 scars few, in an irregular, oblicjue line in the beak-cavity. 



Me.\surements. 



