Pinna. MOLLUSCA. TRIGONIADiE. 407 



Length 5, breadth 2 inches ; corneous, brittle, gloss}'. On the open side 

 the contour not rounded till near the broad extremity. 



416. V.papyracea. — Shell oval, triangular, with nine remote 

 unarmed ribs. 



Turt. Biv. Brit. 224. t. xx. f. 3 — Coast of Devon. 

 Length -H, breadth 2ith inches ; thin, brittle ; the distant ribs cover near- 

 ly the whole surface ; the anterior margin slightly rovmded ; 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. f. 2. — London Clay. 



2. P. arcwata.— Nearly equilateral, ventricose, finely ribbed, arched. — Soicer. 

 Min. Conch, t. 313. f. 3 — Lcmdon Clay. 



3. P. lanceolata. — Lanceolate, slightly curved, longitudinally striated, sec- 

 tion quadrangular. — Sower. Min. Conch, t. 281 Inferior Oolite. 



4. P. tetragona.-^'Narrow, smooth, or obscurely ribbed, prismatic ; valves 

 longitudinally carinated with a suture in the middle. — Sower. Min. Conch, 

 t. 313. f. 1. — Green Sand and Oolite. 



5. p. ffranulata. — Broad, nearly equilateral, convex, obscurely decussated, 

 with a small elevation in the centre of each division ; anterior side rounded. 

 Soiver. Min. Conch, t. ^AT .-—Oolite. 



G. V.flahellifwmis. — Somewhat fan-shaped, beaks pointed ; broad end round" 

 ed ; surface with narrow longitudinal ribs, and broad, shallow, smooth fiu'- 

 vows.— M«r^ Derb. t. vi. f. 1, 2. — Carlonifermis Limestone. 



