74 THE CHICAGO ACADEMY OF SCIENCES. 
species. As the shell increases with age, the greenish epidermis 
is replaced by a brownish covering without rays. The females 
generally have a more inflated shell posteriorly than the male. 
Mr. Simpson remarks as follows on gravid examples of this 
species which he has examined: “I found examples of 4. 
ferussaciana in which all four of the gills were filled with 
embryos, the outer enormously distended, the inner moderately 
filled. I have found others in which only the outer gill was 
filled, and still others with the outer gillonly partly filled. The 
inner gill may empty first or it may be filled only under favora- 
ble circumstances.” 
14. Anodontoides subcylindraceus Lea, pl. iv., fig. 4; pl. vi., fig. 1. 
Anodonta subcylindracea Lea, Trans. Amer. Phil. Soc., 2d series, Vol. VI., 
p. 106, pl. xxiv., fig. 117, 1839. 
Shell: Somewhat thin, subcylindrical or elliptical, rounded 
before and triangulate behind, the apex of the angle truncated or 
rounded; dorsal and ventral margins nearly straight in the 
female, and ventral border rounded in the male; surface marked 
by distinct lines of growth, with several dark lines marking 
former rest periods; umbones but little elevated, rusty brown 
or greenish goldin color, but generally eroded, and with four 
small distinct elevated ridges, directed anteriorly; posterior slope 
almost flat, subangulated, but not much excavated; ligament 
rather short, narrow, dark horn color; epidermis greenish or 
greenish yellow, varying from plain to rayed, the green rays being 
numerous, rather wide, and radiating from the umbones to the 
ventral border; hinge line straight, a trifle thickened, with a bare 
indication of cardinal teeth anterior to the umbones; muscle scars 
and pallial line distinct but not impressed; cavity of the beaks 
shallow; nacre silvery white, with a shade of bluish, sometimes 
pure white under the beaks, iridescent. 
Length, 69.00; height, 36.00; breadth, 26.00 mill. ¥ (12948). 
4: 65/005..." “es 82.00; ‘ 24.50 ‘* © (coll. Jensen). 
4 74.00; ‘ 38.00; 29.50 ‘* ¥$ (13032). 
Animal; Generally whitish or yellowish; mantle white edged 
with brownish black, the tentacular portion darker; ctenidia 
long and narrow, rounded at both ends and united above their 
entire length, yellowish in color; labial palpi rounded, not large, 
united at base, yellowish in color; foot of good size, whitish or 
yellowish; the abdomen whitish; tentacles small, blackish 
