PLATE 58. 



Page 

 Figs. 1 - 21. Pentamerella arata 375 



1. Dorsal view or 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 fiu.\uo8C plications. 



10. Cardinal view of a large cast, showing the cavities led 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. GrpiDtJLA L.a!vnJ8CULA 381 



22, 23. Dorsal and ventral views of a specimen of this species. 



Figs. 24, 25. Penta-merella obsolescens 379 



24, 25. Exterior and interior of a dorsal valve of this species, showing the small tri.ingular pit 

 and the fiattened space or area on each side of it. 



Figs. 26, 27. Pentamerella micula 378 



26. Exterior of a dors.il valve of the species. 



27. Interior of a dorsal valve, showing the triangular pit. 



Figs.28-37. Pentamerella PAPILI0NEN8IS 377 



28. 29. Dorsal views of small individuals of the usual form. 



80. View of a dorsal valve where the plications are somewhat angular, as in many e.vamples of 



p. arata. 

 81-34. Dorsal, ventral, profile and front views of a full grown and characteristic individual. 

 86. Ventral valve of a crushed specimen, showing irregular plications and strong concentric 



lines of growth. 



36. View 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 879 



38. 39. Dorsal and ventral valves of a small individual. 



40-43. Dorsal, profile, cardinal and fVont views of a large and characteristic specimen of the 

 species. 



