PLATE LXXVII. 
1. Pectunculus Brevirostris. (Short-beaked Pectunculus.) Orbicular, oblique, inequilateral, convex; hinge-line triangular; 
teeth few; beaks short, obtuse, approximating; surface, with flat, longitudinal ribs, crossed by concentric strife. 
2, 3, 4. P. Minimus. (Least Pectunculus.) Orbicular, convex, equilateral; liinge-lino straight, with about five teeth; beaks 
prominent ; surface smooth. 
5. P. Pilosus. (Hairy Pectunculus.) Orbicular, convex; beaks large, rounded, close ; hinge-area large, with triangular linos; 
teeth many; surface, with fine strife, crossed by remote lines of growth. 
6, 7, 8. P. OblongUS. (Oblo)ig Pectunculus.) Transversely ovate, inequilateral, convex; sides truncated ; surface smooth. 
9. P. Obliquus. (Oblique Pectunculus.) Sub-ovate, compressed; beaks small, close; ligament-area triangular; teeth of hinge 
many ; surface, with many, longitudinal strife, crossed by man}-, concentric ones ; with small marginal crenulations ; shell thin. 
10. P. Sublsevis. (Half-smooth Pectunculus.) Orbicular, equilateral, convex; beaks short, close, rounded ; surface, with many, 
obtuse ribs; sides smooth ; inner edge crenulated. 
11. P. Umbonatus. (Large-beaked Pectunculus.) Orbicular, equilateral, gibbose; beaks large, prominent ; hinge-area large ; 
teeth many ; surface, with fine, longitudinal strife, and obscure, concentric ribs ; inner edge with large crenulations. 
12. Area Carinata. (Keeled Area.) Convex, parallelipedal; anterior side flattened, truncated ; posterior side rounded; surface 
longitudinally ribbed. 
13. P. Delectus. (Delectable Pectunculus.) Orbicular, compressed; hinge, with about fourteen teeth; surface, with about 
twenty-five, sharp ribs and a few, concentric striae; margin crenulated within. 
14. P. Plumsteadiensis. (Plumstead Pectunculus.) Sub-orbicular; one side straight; beaks produced; hinge straight, with 
many teeth; surface, with faint, longitudinal sulci, with minute, concentric strife ; margin internally crenated. 
15. A. Tumida. (Tumid Area.) Gibbose, transversely elongated ; anterior side acute; marginal sinus short, deep ; umbones 
remote ; surface, with obsolete ribs. 
16. A. Branderi. (Brander's Area.) Transversely elongated, gibbose; boaks remote; hinge-liue straight; with obtuse ridge 
from beak ; space between beaks, with three or four impressed strife ; surface finely decussated ; teeth many; external edge entire. 
17. A. Appendiculata. (Appendaged Area.) Transversely elongated, rhombic, gibbose ; beaks distant, incurved ; with two, 
oblong appendages on hinge-area ; surface decussated; longitudinal ridges furcated ; internal margin toothed. 
18. A. Cancellata. (Cancellated Area.) Transversely elongated; beaks produced, close ; anterior side defined by keel; marginal 
sinus short, deep ; surface, with longitudinal and transverse strife, cancellated. 
19. A. Duplicata. (Two-plaited Area.) Convex-ovate, transversely elongated, with double, longitudinal ribs, furcated in centre; 
margin toothed ; marginal sinus obscure ; beaks close. 
20. P. Decussatus. (Decussated Pectunculus.) Sub-orbicular; sides straight; compressed; hinge, with from twenty-five to 
thirty teeth ; beaks small, obtuse; surface, with many, lougitudinal strife ; margin thick, entire. 
21. Cucullaea Contracta. (Contracted Cucullcea.) Sub-quadrangular, inflated ; beaks largo, obtuse ; base straight ; surface 
smooth. 
22. C. Rudls. (Rough Cucullcea.) Convex, transversely oblong; beaks incurved, close ; surface rough, longitudinally ribbed ; 
anterior lobe ill-defined ; disc striated. 
23. P. Scalaris. (Ladder Pectunculus.) Obovate ; beaks prominent; hinge-line short, with triangular pit in centre ; centre of 
surface, with strong ribs ; internal margin finely crenulated. 
24. A. Depressa. (Depressed Area.) Compressed, transversely elongated; sides rounded ; surface, with distant, crenulated 
strife, decussated by lines of growth; marginal sinus obscure. 
25. C. Oblonga. (Oblong Cucullcea.) Gibbose, transversely oblong ; anterior side cuneiform; beaks incurved ; hinge-area 
rhomboidal, with from nine to twelve parallel lozenges ; surface, with many, longitudinal striae. 
26. A. Rotundata. (Rounded Area.) Transverse; beaks small, close; anterior side narrow; surface, with fine, longitudinal 
striae, and a few, concentric lines of growth. 
27. A. Eastnori. (Eastnor's Area.) Thick, transversely ovate, convex; beaks short, central; hinge-line rectilinear; teeth 
small, upright, many. Length, ^ in. ; breadth, 1 in. 
28. A. Papillosa. (Pimpled Area.) Transversely elongated; beaks produced, incurved, remote; hinge-line long, straight, with 
many, small teeth ; posterior side truncated ; basal and hinge-lines parallel; surface, with many, papillose ribs, and a few transverse 
lines of growth. 
29. A. Pulchpa. (Splendid Area.) Elongated, transversely ovate, depressed; auterior side impressed, truncated; beaks close ; 
surface, with close, uniform strifB. 
30. A. Quadrisulcata. ( Four-furrowed Area.) Convex; anterior side truncated, defined by a keel, with four, deep sulci; 
margin, with large sinus ; surface, with longitudinal striae, crossed by lines of growth. 
31. 32. A. Costata. (Ribbed Area.) Transversely oblong-ovate; anterior side short, acute; posterior side sub-truncated; 
beaks small ; surface, with three or four ribs, with many, faint, concentric wrinkles. 
33. A. Subacuta. (Sub-acute Area.) Gibbose, transversely oblong ; surface, with longitudinal strife ; marginal plaits rounded, 
deep ; teeth sharp, many. 
34. A. Elongata. (Elongated Area.) Transversely elongated; beaks obtuse; posterior side sub-truncated ; hinge-lino and 
base parallel ; surface, with longitudinal stri®, crossed by remote lines of growth. 
35. A. Dubia. (Doubtful Area.) 
36. A. A2mula. (Emulating Area.) Transversely elongated; beaks large, obtuse, close; disc hollowed; surface, with 
longitudinal striae, crossed by transverse lines of growth. 
37. 38. C. Minuta. (Minute Cucullaea.) Convex, ovate, elongated; ridge dividing anterior lobe making angle on margin; 
anterior side truncated; beaks close ; surface, with longitudinal striae. 
39. C. Crassatina. (Thickened Cucullcea.) Gibbose, transversely ovate; anterior side angular; surface, with flattened, 
longitudinal ridges, decussated by lines of growth ; interior margin crenated. 
40. C. Fibrosa. (Fibrous Cucullcea.) Gibbose, ovate ; anterior margin straight, prominent; surface, with many, lougitudinal 
striae, crossed by lines of growth. 
41. C. Carinata. (Keeled Cucullcea.) Cuneiform; anterior side pointed, with ridge from beaks to margins ; surface smooth. 
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