386 MOLLUSCA. BIVALVIA. Pecten. 



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

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

 —Sower. Min. Conch, t. lvi. f. 4-8. — In Chalk 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 — Soiver. Min. Conch, t. cxxxvi. f. i. — Under Oolite. 



4. Y.Jibrosus — Depressed, orbicular, with a rectangular beak, nine or ten 

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

 rectangular ; margin undulated internally — Soiver. Min. Conch, t. cxxxvi. 

 f. 2 Under Oolite. 



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

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

 — Chalk Marl. 



6. P. orbicularis. — Orbicular, "much depressed, concentrically striated ; stria; 

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

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



I. P. corneus — Orbicular, much depressed, smooth ; ears small, nearlv 

 equal; two obtuse teeth near the ear within each valve. — Sower. Min. 

 Conch, t. cciv. — London Clay. 



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

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

 Oolite. 



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



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

 Oolite. 



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

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

 t. ccv. f. 4. — Under Oolite. 



II. P. arcuatus Orbicular, depressed, with arched, punctured, and diver. 



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

 arched. — Sower. Min. Conch, t. ccv. f. 5-7 — 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. Y.rigidus. — Orbicular, depressed; strongly striated ; striae arched, di- 

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



Under Oolite. 



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

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

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



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



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

 Min. Conch, t. ccxxxix — Upper Oolite. 



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

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

 thin. — Sower. 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 subtubular imbricated scales ; margin internally fim- 

 briato-crenated ; ears distinct, nearly equal — List. Conch, t. cccclxx.— Sower. 

 Min. Conch, t. ccclxx. 1'. 1 — In Green Sand. 



