MARINE MOLLUSCA OP THE UNITED STATES. 133 



Genus PERIPLOMA, Schum. 

 Essai Nov. Gen. 115. 1817. 

 Cochlodesma, Couthouy. Bost. Journ. Nat. Hist., ii. 170. 1839. 



1. P. PAPYRACEA, Say. Fig. 298. 



(Anatina.) Journ. Philad. Acad., ii. 314. 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. Piilad. Acad., vi. 263, t. 11, f. 11. 

 Coclilodesma 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 Ooast. 



I do not acquiesce in the separation of this species from Peri- 

 ploma, as I do not find sufficient distinctive characters for a 

 different genus. The absence of the ossiculum does not appear 



