102 THE CHICAGO ACADEMY OF SCIENCES. 
Shell: Large, elongated, compressed, thick and heavy, 
rounded before, pointed-triangular behind; dorsal margin nearly 
straight; ventral margin slightly rounded, much produced pos- 
teriorly in the female; surface smooth and shining, growth lines 
well marked, imbricated on the lower half of the shell and more 
or less on the anterior and posterior ends; umbones depressed, 
inflated, brownish, rather small, marked by numerous fine ridges; 
anterior umbonal slope rounded; posterior slope rounded near 
the posterior part of the shell, but more or less angular near 
the umbones; ligament long, wide, stout, very dark brown or 
black; epidermis corneous or blackish, with a reddish tinge, 
obscurely rayed with broad, dark green bands of color, which 
disappear in old specimens; cardinal teeth double in both 
valves, those in the left valve about equal in size, the anterior 
tooth in the right valve generally very small, but by an enlarge- 
ment of the hinge line, sometimes quite large and elevated; 
teeth generally posteriorly recurved and erect, stout, triangular 
and heavily serrated, sometimes thin, sharp, very much elevated 
and serrated; lateral teeth long, straight, lamelliform, elevated, 
crenulated; anterior adductor muscle scar wing shaped, longer 
than wide, very deeply excavated, striated; posterior adductor 
muscle scar rounded, diameters equal, generally, distinct but 
hardly impressed, concentrically striated; protractor pedis muscle 
scar wider than long, very deeply impressed, striated; pallial line 
crenulated, deeply impressed anteriorly; dorsal muscle scars 
situated in the center of the cavity of the beaks, large, oval, 
forming deep pits; cavity of the beaks very shallow; nacre sil- 
very white or dark purple, and exhibiting all variations between 
these two colors; some specimens are white about the ventral 
and anterior and posterior portions, and deep purple or pink in 
the region beneath the hinge teeth. 
Length, 106.00; height, 45.00; breadth, 27.00 mill. ¢ (9718). 
1176:00; . 0° /2-GR00: n 33.00 ‘ GJ (12440). 
Animal: Anal opening small, without papille; branchial 
opening moderate, with many irregular papille; mantle edge 
thick and doubled; outer edge plain, inner with beautiful regu- 
lar teeth on posterior half; inner gill the larger, united nearly 
the whole length to abdominal sac; branchial uterus occupying 
position two fifths of outer branchia in thirty-two distinct ovi- 
sacs. (Simpson. ) 
