THE NATURAL HISTORY SURVEY. 87 
Shell: Orbicular, sometimes inclining to quadrate, inflated, 
thick, heavy; dorsal border slightly curved, ventral border 
curved; rounded before, broadly rounded or truncated behind; 
surface roughened by lines of growth and marked with pustules, 
which may be very few or very numerous, and may fill the entire 
valve or only asmall portion of it; the pustules vary in size and 
are either small or rounded knobs or long and narrow ridges; 
anterior umbonal slope rounded, posterior slope flattened or 
rounded, sometimes excavated; umbones varying from elevated 
to depressed, inflated, light greenish or brownish, marked by 
about four elevated ridges and numerous fine growth lines; the 
umbones are almost always eroded; ligament short, wide, stout, 
very dark horn, sometimes striped with a still darker color; 
epidermis varying from a uniform yellowish brown to yellowish 
with a broad band of dark green extending from the umbones 
to the ventral border, widening as it nears the latter region; in 
some specimens the green color is disposed on different parts of 
the shell in small patches; cardinal teeth double yn both valves, 
equal in the left, the posterior the larger inthe right valve, solid, 
triangular, deeply grooved, diverging; the cardinals are very 
variable, being wide or narrow, elevated or depressed, single or 
double, sulcated or almost smooth, and furnished with a number 
of accessory toothlets; lateral teeth short, stout, lamellar, ele- 
vated, serrated, directed ventrally; connecting bridge wide, thick, 
smooth or sulcated; anterior adductor muscle scar elliptical, 
very deeply excavated, strongly striated; posterior adductor 
muscle scar rounded, impressed, confluent, iridescent; protractor 
pedis scar as usual; dorsal muscle scars situated on the posterior 
face of the cardinal teeth, numerous, arranged ina straight line, 
deeply pitted; pallial line impressed, imbricated; cavity of the 
beaks deep; nacre pearly white, iridescent onthe posterior region. 
Length, 59.50; height, 58.00; breadth, 36.25 mill. (7763). 
bebe ae 54.50; HI. 82.00 ' (7763). 
oa O04 as 39.00: “ 32.00 ‘ © (18444). 
Animal: Generally flesh colored, lighter and darker in 
places; ctenidia short and wide, half-moon shaped, rounded at 
both ends, chocolate brown in color, united above and to the 
opposite pair for their entire length; the inner ctenidium is much 
the larger, and both are thickened posteriorly; labial palpi short, 
wide, ovate, adherent at base, in color like the ctenidia; foot 
whitish, tinged with yellowish or salmon; anal opening small, 
