Pinna. MOLLUSCA. TRIGONIADtE. 407 
Length 5, breadth 2 inches ; corneous, brittle, glossy. On the open side 
the contour not rounded till near the broad extremity. 
416. Px papyracea . — Shell oval, triangular, with nine remote 
unarmed ribs. 
Turt. Biv. Brit. 224. t. xx. f. 3.— Coast of Devon. 
Length 4|, breadth 2|th inches ; thin, brittle ; the distant ribs cover near- 
ly the whole surface ; the anterior margin slightly rounded ; contracted ra- 
pidly towards the apex ; the open end even. 
EXTINCT SPECIES. 
1. P. affinis Cuneiform, ventricose, straight, longitudinally ribbed, rather 
thick, smooth. — Sower. Min. Conch, t. 313. 1. 2. — London Clay. 
2. ' P. arcuata. — Nearly equilateral, ventricose, finely ribbed, arched.— 
Min, Conch, t. 313. f. ^.-—Londm Clay. 
3. P. lanceolata — Lanceolate, slightly curved, longitudinally striated, sec- 
tion quadrangular. — Sower. Min. Conch, t. 281. — Inferior Oolite. 
4. P. Narrow, smooth, or obscurely ribbed, prismatic ; valves 
longitudinally carinated with a suture in the middle. — Sower. Min. Conch, 
t. 313. f. \.~^Green Sand and Oolite. 
5. P. granulata. — Broad, nearly equilateral, convex, obscurely decussated, 
with a small elevation in the centre of each division ; anterior side rounded. 
Sower. Min. Conch, t. •^Oolite. 
6. V.flahelliformis. — Somewhat fan-shaped, beaks pointed ; broad end round” 
ed; surface with narrow longitudinal ribs, and broad, shallow, smooth fur« 
rows.— Mar#. Derb. t. vi. f. 1, — Carboniferous Limestone. 
