586 MEMOIRS OF THE CARNEGIE MUSEUM. 



middle of the disk and toward the beaks, sHghtly lamellar and more crowded on 

 the posterior slope and near the lower margin. Upon the main part of the disk 

 there are traces of indistinct radial hnes. Posterior slope with an indistinct radial 

 ridge. Color of epidermis j^ellowish brown, lighter in anterior half of the shell, 

 darker in the posterior, the two colors divided by a rather distinct radial boundary- 

 line through the middle of the shell. No color-rays are visible. 



Hinge-line straight behind the beaks. In front it is curved down, and then 

 it slopes up again, making the lunula slightl}' concave. One pseudocardinal tooth 

 in each valve, that of the left valve standing in front of, and slightly below, that 

 of the right. The former is verticallj' depressed and projects into a slight groove 

 of the right valve. This groove has a low horizontal ridge, fitting into a groove 

 at the base of the upper face of the tooth of the left valve; however, this may be 

 an individual character. Tooth of the right valve subpyramidal, not depressed, 

 projecting and fitting into a groove which is partly imder the margin of the left 

 valve (the stumpy character of this tooth may also be individual). Ligamental 



sinus triangular, about as deep as wide, its anterior margin oblique to the hinge- 

 Ime. 



Nacre white, not very iridescent,-" with hardly any traces of radial lines. 

 Prismatic zone comparatively narrow, slightly wider in the anterior part of the 

 shell, but not abruptly widening anywhere. 



Cavity of shell shallow, that of beaks moderate. Anterior adductor-scar 

 sharply marked, elliptical. Anterior retractor-scar above it and close to it, but 

 separated; in the right valve it appears double. Anterior protractor-scar con- 

 nected with adductor-scar. Posterior adductor-scar less sharplj^ marked, subovate, 

 with a triangular process above formed by the posterior retractor-scar. No dorsal 

 scars. Pallial line subconcentric to margin. 



Measurements. 



Hrijiht. I Diameter. Beaks. Greatest Height. Figured. 



cf 102 mm.|79 mm. =77 pr. ct. of L. 46 mm. =45 pr. ct. of L. at .38 mm. =37 pr. ct. of L. at 48 mm. =47 pr. ct. of L. PI. XLI, 



_i I , ^ I \_ I f5(j. 1. 



Remarks. — A verj'^ striking and certainly new species, although only a single 

 individual is at hand. It is much larger than any of the known species, and has 

 a shape characterized chiefly by the location of the greatest height in front of the 

 middle, and the absence of a distinct narrowing of the anterior part of the shell. 



-^ The nacre apparently is slightly c(jrroded. Although the specimen wa.s alive when found, and 

 preserved with the soft parts, the uppermost layer of the nacre has been injured and is e>doliating. Ac- 

 cording to my experience, this happens when specimens are allowed to die before they arc put in alcohol. 



