or 
ws 
THE CHICAGO ACADEMY OF SCIENCES. 
strong, elevated, wavy wrinkles, which are arranged in two par- 
allel rows, forming a double loop; ligament strong, dark horn 
color; epidermis variable in color, in the young it may be light 
greenish with faint indications of rays (sometimes stronger), 
while in the adult it is dark green, blackish or (rarely) reddish, 
with very faint diverging rays; umbonal slope rounded; hinge 
line slightly curved, a trifle thickened; adductor muscle scars 
and pallial line distinct but not impressed, iridescent; protractor 
pedis muscle scar distinct; dorsal muscle scars situated on the 
anterior face of the cavity of the beaks, deeply impressed and 
strongly striate; cavity of the beaks shallow, inflated; nacre 
silvery white in the young, but changing to purple in old speci- 
mens; iridescent. 
Length, 128.00; height, 71.00; breadth, 52.00 mill. < ( 9297).* 
Ke 128.00; f 74.00; sid 55.00 ‘' 3 ( 9528). 
~ 96.00; a 48.00; a AZ OG 208 3 ( 9528) 
w 75.00; Le 48.00; oe 29.50 *' di ( 9842) 
ch 116.00; Ky 67.00; “ 45:50 " © ( 8419). 
ue 76.00; d 46.00; os 29.00 " — (12417). 
Animal: Generally pinkish white, sometimes yellowish, 
spotted with blackish dots about the abdomen; liver brown; — 
gills yellowish white; tentacular portion of mantle dark brown- 
ish black; labial palpi yellowish brown, not large, tongue- 
shaped, united only for a short distance along the dorsal 
margin; gills (cfenidia) large, the outer one smaller than the 
inner, united above throughout their entire length, rounded 
anteriorly and posteriorly; adductor muscles large and power- 
ful; mantle transparent, somewhat vitreous; branchial and 
cloacal siphons large, the former lined with numerous dark 
brownish black tentacles, the latter plain. The pericardium, 
containing the heart, is situated somewhat toward the posterior 
end, and the pulsations are somewhat peculiar in some of the 
specimens examined; there is first a short, quick pulsation, fol- 
lowed immediately by a long, slow pulsation; the writer counted 
thirteen short and thirteen long pulsations, twenty-six in all. 
In several other specimens fifteen regular pulsations were 
counted. The latter is probably normal. 
A curious little parasite belonging to the genus Diplodontus 
(family Hydrachnidz) infests the mantle cavity of this species. 
*In measuring the pelecypods in this report the distance from the anterior to the posterior 
is called length, that from umbones to ventral border, height, and the diameter between 
the valves at their widest part, breadth. This differs from Dr. Lea’s method, he calling the 
present height the length. 
