Pinna. MOLLUSCA. TRIGONIAD^E. 407 



Length 5, breadth 2 inches ; corneous, brittle, glossy. On the open side 

 the contour not rounded till near the broad extremity. 



416. F \ papyracea. — Shell oval, triangular, with nine remote 



unarmed ribs. 



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



Length 4a, breadth 2±th inches ; thin, brittle ; the distant r&s 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. f. 2. — London Clay. 



2.' P. arcua ta.— Nearly equilateral, ventricose, finely ribbed, arched. — Sower. 

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



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

 lion 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. I.— -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. 347— Oolite. 



6. "P.jlabelliformis. — Somewhat fan-shaped, beaks pointed ; broad end round" 

 ed ; surface with narrow longitudinal ribs, and broad, shallow, smooth fur. 

 rows—Mart. Derb. t. vi. f. 1, 2. — Carboniferous Limestone. 



