PLATE LXXVIII. 



PhIHOMA CYLINDEICA. 

 Page 473. 

 Figs. 1, 2. Two rig-ht valves showing the ordinary form of this species. 



Hamilton group. Pompey Hill and share of Cayuga lake, Onondaga Co., N. T. 

 Figs. 3, 4. Two left valves of somewhat ditleront proportions from the preceding specimens. 

 Hamilton grouj). Oiwndaga Co., M. ¥. 



Phthonia nodicostata. 



Page 474. 

 Fig. 5. A small right valve. 



Hamilton group. SJtore of Catiandaigua lake, iV. 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 chai'acter 

 of the ra<iii. 



Phthonia sectifkons. 



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 fonu and surface characters. 



Hamilton group. Cazeyunria, N. Y. 



Fig. 13. A specimen retuning both valves in conjunction. .^^i^^ 



Phthonia likata. 



Page 476. 

 Fig. 14. The right valve of the specimen described, as obtained from a gutta-pereha impression, enlarged 

 to three diameters. 



Hamilton group. Slwre of Cayuga lake, Hf. Y. 



Pholadella radiata. 



Page 469. 

 See Plate 96. 

 Figs. lR-18. Two right and two left valves showing the prevailing forms of this species. 

 Fig. 10. Cai-iliiial view of a compn!s.sed s]>ccimen i-etaining both valves. 



Hamilton group. Cazenoma, N. Y. 

 Fig. 20. A right valve of unusually large size. 



Hamilton group. Fahius, N. Y. 

 Fig. 21. An elongate right valve. 



Lower Chemung group. Ithaca, N. Y. 



Pholadella pakallei,a. 



Page 470. 

 Figs. 22, 23. Right and left valves. 



Hamilton gi-oup. Shore of iStkaneateles lake, N. Y. 

 Fig. 24. A portion of a block preserving the remains of numerous individuals of this species. 



Hamilton group. Near Fafnus, N. Y. 



