PLATE 58. 
Page 
Figs. 1 - 21. Pentamerella arata. 375 
1. Dorsal view of a young individual. 
2-4. Ventral, dorsal and profile views of a small well formed individual. 
5.-8. Dorsal, ventral, profile and front views of a characteristic specimen of the ordinary size. 
9. Cast of a large dorsal valve having peculiarly flexuose plications. 
10. Cardinal view of a large cast, showing the cavities left by the removal of the parts of the 
hinge. 
11, 12. Profile and front views of an unusually large and arcuate ventral valve. This and the 
foregoing specimens are all from the Schoharie grit of Albany and Schoharie counties, 
.New York. 
13-16. Dorsal, ventral, profile and front views of a specimen from the Upper Helderberg lime¬ 
stones of New York. 
17, 18. Interior of dorsal and ventral valves, showing the hinge structure, from the Upper Hel¬ 
derberg limestones of New York. 
19. Dorsal view of a specimen from the limestones at the Falls of the Ohio. 
■ 20, 21. Dorsal and ventral views of a specimen from the limestones at Waterloo, Iowa. 
Figs. 22, 23. GtYpidula LjEviuscula... 381 
22, 23. Dorsal and ventral views of a specimen of this species. 
Figs. 24, 25. Pentamerella obsolescens. 379 
24, 25. Exterior and interior of a dorsal valve of this species, showing the small triangular pit 
and the flattened space or area on each side of it. 
Figs. 26, 27. Pentamerella micula. 378 
26. Exterior of a dorsal valve of the species. 
27. Interior of a dorsal valve, showing the triangular pit. 
Figs. 28-37. Pentamerella papilionensis. 377 
28. 29. Dorsal views of small individuals of the usual form. 
30. Yiew of a dorsal valve where the plications are somewhat angular, as in many examples of 
P. arata. 
31-34. Dorsal, ventral, profile and front views of a full grown and characteristic individual. 
35. Yentral valve of a crushed specimen, showing irregular plications and strong concentric 
lines of growth. 
36. Yiew of a specimen where the beak of the dorsal valve has been cut away to show the 
extent of the spoon-shaped process of that valve. 
37. Interior of the ventral valve, showing its spoon-shaped process. 
Figs. 38-43. Pentamerella dubia. 379 
38. 39. Dorsal and ventral valves of a small individual. 
40-43. Dorsal, profile, cardinal and front views of a large and characteristic specimen of the 
species. 
