PLATE LXXVTLI. 
Phthonia cylindrica. 
Page 473. 
Pigs. 1, 2. Two right valves showing- the ordinary form of this species. 
Hamilton group. Pommy Hill and shore of Cayuga lake, Onondaga Co., N. Y. 
Figs. 3, 4. Two left valves of somew-hat different proportions from the preceding specimens. 
Hamilton group. Onondaga Co., N. Y. 
Phthonia nodicostata. 
Page 474. 
Fig. 5. A small right valve. 
Hamilton group. Shore of Canandaigua lake, N. Y. 
Fig. 6. A larger right valve. 
Hamilton group. Near Oneonta, N. Y. 
Figs. 7, 8. Two left valves showing the surface ornamentation characteristic of this species. 
Hamilton group. Shores of Canandaigua and Cayuga lakes, N. Y. 
Fig. 9. An enlargement of a portion of the surface from the specimen fig-. 7, showing the nodose character 
of the radii. 
Phthonia sectifrons. 
Page 475. 
Fig. 10. A small left valve. 
Fig. 11. A large left valve narrowed by compression. 
Fig. 12. A large right valve showing the form and surface characters. 
Hamilton group. Cazenovia, N. Y. 
Fig. 13. A specimen retaining both valves in conjunction. 
Phthonia lirata. 
Page 476. 
Fig. 14. The right valve of the specimen described, as obtained from a gutta-percha impression, enlarged 
to three diameters. 
Hamilton group. Shore of Cayuga lake, N. Y. 
Piioladella radiata. 
Page 469. 
See Plate 96. 
Figs. 15-18. Two right and two left valves showing the prevailing forms of this species. 
Fig. 19. Cardinal view of a compressed specimen retaining both valves. 
Hamilton group. Cazenovia, N. Y. 
Fig. 20. A right valve of unusually large size. 
Hamilton group. Fabius, N. Y. 
Fig. 21. An elongate right valve. 
Lower Chemung- group. Ithaca, N. Y. 
Piioladella parallela. 
Page 470. 
Figs. 22, 23. Right and left valves. 
Hamilton g-roup. Shore of Skaneateles lake, N. Y. 
Fig. 24. A portion of a block preserving the remains of numerous individuals of this species. 
Hamilton group. Near Fabius, N. Y. 
