MOLLUSCA. BIVALVIA. 
Plagiostoma. 
389 
straig'litish ; one valve spinous, spines half the length of the shell — Soiver 
Min. Conch, t. Ixxxiii. — In Chalk. 
3. P. punctatum. — Depressed, obliquely ovate, with numerous diverging 
striae ; anterior side long, straight ; ears nearly equal ; diverging striae trans- 
versely marked with other very fine striae or points. —Sower. Min. Conch, t. 
cxiii. f. 1, 2 — In Lias. 
4. P. cardieforme. — Gibbous, nearly circular, longitudinail}’^ furrowed, 
smooth; anterior side short, straight; wings equal. — Sower. Min. Conch, 
t. cxiii. f. 3 — In Oolite. 
5. P. rigidum — Gibbous, obliquely ovate, with many diverging sharp thread- 
like ribs, and very minute intervening transverse striae ; anterior side long, 
straight, very concave ; ears nearly equal. — Sower. Min. Conch, t. cxiv. f. 1. 
— In Oolite. 
6. P. ovale — -Rather gibbous, oblique, elongated, oval, with many small 
ribs, and minute intervening transverse striae ; anterior side concave, slightly 
recurved. — Smver. 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 Lms. 
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, 3-1 5. — Sower. 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. IcBviusculum Transversely^obovate, oblique, convex, longitudinally 
ribbed ; ribs close, broad, irregular, very little elevated, convex ; anterior 
slope straight, hollow ; ears small, unequal.— S'ozrer. 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. £ \b.~~-Upper Chalk. 
Gen. GRYPHiE 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. mmrm.— Elongated, very involute, right side an obscure lobe ; lesser 
valve oblong, externally concave. — Park. Org. Rem. iii. 209. t. xv. f. 3. — = 
In Lias. 
2. G. obliquata.—Ohlovig., slightly involute, oblique ; right side an obscure 
lobe ; lesser valve irregularly ovate, externally concave.— Min. Conch, 
t, cxii. f. 3. — In Lias. 
