Pecten. MOLLUSCA. BIVALVIA. 387 



18. P. obliquus.— Obliquely oval, convex on both sides; radii very nume- 

 rous, roughened by semicircular imbricated scales ; ears large, distinct — 

 Sower. Min. Conch, t. ccclxx. f. 2 — In Green Sand. 



19. P. cinctus Orbicular, gibbose, longitudinally striated, imbricated 4 



edges of the laminae thin, erect ; ears small ; edge entire. — Soiver. Min- 

 Conch, t. ccclxxi — Under Oolite? 



20. P. sulcatus Obliquely orbicular, with twenty obscurely tripartite 



rays, the intermediate spaces longitudinally striated, the whole rough with 

 minute scales ; internally sulcated ; ears nearly equal. — Sower. Min. Conch, 

 t. cccxciii. f. 1. — Suffolk Crag. 



21. P. gracilis Orbicular, thin, convex, with many small longitudinal 



ridges, concentrically striated ; striae close, elevated, sharp ; ears unequal ,• 

 margin entire. — Soiver. Min. Conch, t. cccxciii. f. 2. — In Crag. 



22. P. strialus. — Oval, convex ; valves nearly equal, with numerous smooth 

 or scaly ridges ; within plain, margin entire ; ears equal, rather large— Sower. 

 Min. Conch, t. cccxciv. f. 2, 3, 4.— In Crag. 



23. P. nitidus -Obovate, one valve nearly flat, with numerous, nearly 



smooth ridges, the interstices minutely striated transversely, the other valve 

 convex, with as many crenulated ridges ; margin entire ; ears nearly equal. 

 — Mant. Suss. 202. t. xxvi. f. 4-9 — Sower. Min. Conch, t. cccxciv. f. 1. — In 

 Chalk. 



24. P. obsoletus ? — Equivalved ; ears very unequal ; surface finely striated ; 

 strise obliquely diverging. — Soiver. Min. Conch, t. Dxli — In Crag. 



25. P. princeps. — Orbicular, compressed ; decorated with ninety rounded 

 nearly equal radii, surmounted with erect concave scales ; ears large, un- 

 equal, squamose ; valves equal. — Soiver. Min. Conch, t. Dxlii. f. 2 — In Crag. 



26. P. annulatus Orbicular, convex 5 numerous thin, erect, concentric 



laminae, and fine longitudinal striae ornament the surface, passing over the 

 large ears Sower. Min. Conch, t. Dxlii. f. 1 — Lower Oolite. 



27. P. vimineus Convex, rather longer than wide, concentrically striated j 



rib.* about twenty, prominent, close beset with thick elevated scales, which 

 are less numerous upon the left valve ; ears nearly equal. (P. varius, Geol. 

 Surv. Yorksh. 223. t. ix. f. 9.)— Sower. Min. Conch, t. Dxliii. f. 1, 2 — Lower 

 Oolite. 



28. P. vagans Ilather convex, a little longer than wide ; ribs eleven, 



large, convex, decorated with large erect concave scales, that are very close 

 upon the right, but distant upon the left, valve ; ears nearly equal, crossed 

 by larger scales.— (P. sulcatus, Geol. Surv. York. 233. t. ix. f. 3.) — Sower. 

 Min. Conch, t. Dxliii. f. 3, 4, 5 — Lower Oolite. 



29. P. triplicatus Subtriangular, longitudinally striated, with three deep, 



longitudinal furrows, which form angular plicae on the front ; margin crenu- 

 lated Mant. Geol. Suss. 128. t. xxv. f. 9.— In Grey Clialk Marl. 



30. P. laminosus Suborbicular, much depressed, concentrically laminated, 



ears nearly equal. — Mant. Geol. Suss. 128. t. xxvi. f. 8 — In Grey Chalk 

 Marl. 



31. P. dissimilis — Suborbicular, slightly lengthened, the right or lower 

 valve with numerous ribs, slightly scaly ; ears nearly equal, ribbed trans- 

 versely and longitudinally ; the left or upper valve concave, regularly mark- 

 ed concentrically with flat obsolete ribs, which become scaly in crossing the 

 longitudinally l-ibbed ears. In my cabinet, from the shale and limestone of 



the Independent Coal formation In the concavity of the left valve, it agrees 



with the recent P. marinus and P. Jacobanis. 



b b 2 



