MARINE MOLLUSCA OF THE UNITED STATES. 133 
Genus PERIPLOMA, Schum. 
Essai Nov. Gen. 115. 1817.5 
Cochlodesma, Couthouy. Bost. Journ. Nat. Hist., ii. 170. 1889. 
1. P. papyraceA, Say. Fig. 298. 
(Anatina.) Journ. Philad. Acad., ii. 8314. 1822. 
A. fragilis, Totten. Am. Journ. Sci., xxviii. 347, f. 1. 
Shell thin, fragile, rounded-ovate ; one valve more convex and 
at the basal margin projecting a little beyond the other. Beaks 
not prominent, in the posterior third of the length of the shell; 
from the beaks to the posterior margin runs an elevated angular 
ridge; posterior margin narrowed and subtruncated, slightly 
gaping. Exterior surface minutely wrinkled. Tooth long, 
narrow, and oblique, with an accessory process at the base. 
White and pearly. 
Height 12, breadth 17 mill. 
Whole Coast (rare). 
Mr. T. A. Conrad (Am. Journ. Conch., ii. 106) revives Totten’s 
name for the New England shell which he considers to differ from 
Say’s species—the latter being described from the Southern Coast. 
The outline varies considerably in different specimens, and there 
does not seem to be sufficient ground for the separation proposed 
2. P. LEANA, Conrad. Figs. 436, 437. 
(Anatina.) Journ. Philad. Acad., vi. 263, t. 11, f. 11. 
Cochlodesma Leana, Couthouy. Bost. Journ. Nat. Hist. ii. 170. 
Shell very thin and fragile, ovate, subcompressed ; the left valve 
almost flat, rounded at both ends; the right valve convex and 
subtruncate at the shorter end, slightly gaping at both ends. 
Beaks small, slightly cleft at one side; from the beaks proceeds a 
ridge, more or less obvious to the posterior end. Surface 
wrinkled, with a yellowish shining epidermis extending somewhat 
beyond the margins; the spoon-shaped process in the hinge 
nearly horizontal, and resting on an oblique rib directed back- 
wards; no ossiculum. 
Vertical axis 22.5, transverse axis 32.5 mill. 
Laminarian. Whole Coast. 
I do not acquiesce in the separation of this species from Per?- 
ploma, as I do not find sufficient distinctive characters for a 
different genus. The absence of the ossiculum does not appear 
