84 THE CHICAGO ACADEMY OF SCIENCES. 
excavation spoken of above; the anterior set of pustules is 
arranged in a narrow line, but the posterior set covers all of the 
posterior part where they are long and narrow and directed 
toward the posterior border; the majority of the pustules are 
small and rounded, but there are one or two very large ones 
near the ventral and central part which are longer than wide; 
the pustules are more numerous about the umbonal region than 
on any other part of the shell and the anterior part of the shell 
is always free from them; umbones small, compressed, light 
brown, marked by numerous small pustules; anterior umbonal 
slope rounded, posterior slope pustulose, forming an angle; 
ligament short, wide, solid, very dark brown; epidermis yel- 
lowish green, obscurely rayed with dark green; cardinal teeth 
stout, triangular, diverging, heavily grooved, double in both 
valves as in vefiexa; lateral teeth long, narrow, serrated, 
directed ventrally; connecting bridge solid, flat, smooth; anterior 
adductor muscle scar forming a_ truncated oval, deeply 
impressed, striated; posterior adductor muscle scar scarcely 
visible, confluent; Avotractor pedis muscle scar oval, deeply 
impressed, striated; dorsal muscle scars numerous, small (large 
exceptionally), deeply pitted, situated on the posterior face of 
the cardinal teeth and on the under side of the connecting 
bridge; pallial line impressed, especially anteriorly, crenulated; 
cavity of the beaks deep; nacre silvery white, iridescent, espe- 
cially on the posterior part of the shell. 
Length, 60.00; height, 47.00; breadth, 28.00 mill. (9696). 
“68.00; = 58.50; ' 25.00 “ (18088). 
“86.00; ‘ 70.00; ‘ 39.00 * (18442). 
“30.00; 21.00; = 18.00 * (18442 juv.) 
Animal: Pearly white, tinged with flesh color; ctenidia 
small, long and somewhat narrow, rounded at both ends, the 
inner one the larger, united above for their entire length, but 
the opposite pair united to its fellow pair for but three-quarters 
of the distance; color of gills light flesh; labial palpi of same 
color as gills, large and wide, tongue shaped, united at base; 
foot rather large, flesh colored; abdomen pearl colored, tinged 
with flesh, sometimes iridescent; mantle pearly or flesh colored, 
with a line of pearl colored vertical fibers running clear around 
near the border; the ventral border edged with brown; anal and 
branchial openings large, brownish, the former crenulated and 
the latter papillose; liver brownish; heart very active and 
