Plagiostoma. MOLLUSCA. BIVALVIA. 389 



straightisli ; one valve spinous, spines half the length of the shell Sotver 



Min. Conch, t. Ixxxiii. — In Chalk. 



3. p. punclatum. — Depressed, obliquely ovate, with numerous diverging 

 striie ; anterior side long, straight ; ears nearly equal ; diverging striae trans- 

 versely marked with other very fine striae or points. —S'ower. Min. Conch, t. 

 cxiii. f. 1, 2 In Lias. 



4. P. curdleforme. — Gibbous, nearly circular, longitudinally furrowed, 

 smooth ; anterior side short, straight ; wings equal. — Sower. Min. Conch. 

 t. cxiii. f. 3 — In Oolite. 



5. V.rigidum. — Gibbous, obliquely ovate, with many diverging sharp thread- 

 like ribs, and very minute intervening transverse strife ; anterior side long, 

 straight, very concave ; ears nearly equal. — Sower. Slin. Conch, t. cxiv. f. 1. 

 — In Oolite. 



G. P. omfe.— Rather gibbous, oblique, elongated, oval, with manv small 

 ribs, and minute intervening transverse striae ; anterior side concave, slightly 

 recurved. — Sower. Min. Conch, t. cxiv. f 3. — In Oolite. 



7. P. obscurum — Rather gibbous, oblique, ovate, smooth, externally ribbed ? 

 with twenty -five internal sulci ; anterior side flattish ; beaks prominent. — 

 Sower. Min. Conch, t. cxiv. f. 2. — In Oolite. 



8. P. pectinoides — Depressed, a little oblique, obovate, rather angular at 

 the back ; beak pointed ; surface with twenty or more carinated ribs, trans- 

 versely striated ; internally plain ; margin toothed. — Sower. Min. Conch, 

 t. cxiv. f. 4 In Lias, 



9. P. Hoperi. — Transversely ovate, oblique, valves convex, obscurely punc- 

 tato-striated ; striae diverging, deepest upon the sides ; anterior slope straight, 

 concave — Mant. Suss. 204. t. xxvi. f. 2, 3-15 — Soiver. Min. Conch, t. ccclxxx. 

 — In Chalk. 



10. P. rusticum. — Transversely oblong, oblique, longitudinally sulcated ; 

 valves convex ; sulci deep ; ears obscure ; anterior slope straight, convex 

 along the middle. — Sower. Min. Conch, t. ccclxxxi. — In Oolite. 



11. P. IcBviusGulum Transversely^obovate, oblique, convex, longitudinally 



ribbed ; ribs close, broad, irregular, very little elevated, convex ; anterior 

 slope straight, hollow ; ears small, unequal. — Sower. Min. Conch, t. ccclxxxii. 

 — In Oolite. 



12. P. Brightoniensis — Obovate, depressed, longitudinally costated ; pos- 

 terior side eared ; anterior side lunulate, concave, small, acuminated ; mar- 

 gin crenulated — Mant. Suss. cciv. t. xxv. f. \b.— -Upper Chalk. 



Gen. GRYPH^ a. — Inequivalve ; larger valve concave ; with 

 a large involutely curved subspiral beak ; lesser valve nearly 

 flat ; hinge a transversely striated pit, with an internal li- 

 gament. 



1. G. iracwrva..— Elongated, very involute, right side au obscure lobe ; lesser 



valve oblong, externally concave Park. Org. Rem. iii. 209. t. xv. f. 3 



In Lias. 



2. G. obliquata. — Oblong, slightly involute, oblique ; right side an obscure 

 lobe ; lesser valve irregularly ovate, externally concave. — Sower. Min. Conch, 

 fc. cxii. f. 3. — In Lias. 



