386 MOLI.USCA. BIVALVIA. Pecten. 



toothed ; convex valve gibbous, ribbed, principal costse 6, with 4 lesser ones 

 between each ; surface finely transversely striated ; upper valve flat-toothed. 

 — Sower. Min. Conch, t. Ivi. f. 4-8 — In Clmlk and Green Sand. 



3. P. aquivalvis. — Lenticular, with rounded diverging ribs, and many acute 

 concentric striae ; valves equally convex, the lower one smoothest ; ears 

 equal. — Sower. Min. Conch, t. cxxxvi. tl i. — Under Oolite. 



4. V.fibrosus — Depressed, orbicular, with a rectangular beak, nine or ten 

 broadish diverging grooves, and numerous sharp concentric striae ; ears equal, 

 rectangular ; margin undulated internally. — Smver. INIin. Conch, t. cxxxvi. 

 f. 2 Under Oolite. 



5. P. Beaveri. — Depressed, orbicular, smooth, with irregular longitudinal 

 costse ; ears as wide as the shell, nearly equal. — Sower. Min. Conch, t. clviii. 

 —Chalk Marl. 



6. P. orbicularis. — Orbicular,'much depressed, concentrically striated ; striae 

 elevated, sharp ; one valve smooth ; ears nearly equal, broadest at the base. 

 Sower. Min. Conch, t. clxxxvi. — In Green Sand. 



7. P. corneus — Orbicular, much depressed, smooth ; ears small, nearly 

 equal ; two obtuse teeth near the ear within each valve. — Smcer. Miii. 

 Conch, t. cciv. — London Clay. 



8. P. obscurus — Suborbicular, depressed, with obscure arched longitudinal 

 . rug03 upon the surface ; ears large. — Soiver. Min. Conch, t. ccv. f. 1 Under 



Oolite. 



9. P. lens. — Orbicular, convex ; surface marked with diverging arched 



strije ; striae deeply punctured — Sower. Min. Conch, t. ccv. f. 2, 3 Under 



Oolite. 



10. F. laminatus. — Suborbicular, depressed, striated; striae arched, diver- 

 ging ; ears triangular, unequal ; the largest plaited. — Sower. Min. Conch. 

 t. ccv. f. 4. — Under Oolite. 



11. P. arcuatus. — Orbicular, depressed, with arched, punctured, and diver- 

 ging strife upon the surface ; ears large ; the side beneath the largest is 

 arched. — Soiver. Min. Conch, t. ccv. f. 6-7 — Middle Oolite. 



12. p. similis. — Suborbicular, depressed, striated; striae arched, diverging; 

 ears unequal ; sides straight. — Sower. Min. Conch, t. ccv. f. 6. — Under Oolite. 



13. P. rigidus. — Orbicular, depressed ; strongly striated ; striae arched, di- 

 verging; ears large, unequal, decussated. — Sower. Min. Conch, t. ccv. f 8 



Under Oolite. 



14. V.larbatus Orbicular, depressed, transversely striated; rays four- 

 teen, those upon one valve spinose ; spines long, acute, depressed ; ears 

 nearly equal. — Sower. Min. Conch, t. ccxxxi — Under Oolite. 



15. P. lamellosus Orbicular, convex, with concentnc erect lamellae upon 



the surface, and diverging striae near the beaks ; ears large, distinct — Sower. 

 Min. Conch, t. ccxxxix. — Upper Oolite. 



16. V.papyraceus Depressed, obliquely oval, with large unequal rectangu- 

 lar ears ; numerous elevated striae, decussated by the lines of growth ; shell 

 thin. — Soiver. Min. Conch, t. cccliv. — In shale of the Coal formation. 



17. P. asper. — Nearly orbicular, convex on both sides, bearing about seven- 

 teen sets of rays (from five to seven in each, according to the age of the 

 shell), roughened by subtubulav imbricated scales ; margin internally fim- 

 l)riato-crenated ; ears distinct, nearly equal — List. Conch, t. cccchi's..— Sower. 

 Min. Conch, t. ccclxx. f. 1 — In Green Sand. 



