398 NEW YORK STATE MUSEUM 



PLATE 5 



Genus pterochaenia gen. nov. 



[See- pi. 4] 

 Page 247 



Pterochaenia fragilis Mall (sp.) 



Page 249 



i Two valves expanded and juxtaposed along the posterior 

 margin. X3 

 Naples subprovince Naples 



2 A similar specimen. X2 



Genesee shale Bristol 



3 A right valve with expanded byssal flange. X3 



Naples subprovince Naples 



4 A left valve. X3 



Genesee shale Moscow 



5 Interior of left valve. X3 



6 Interior of right valve. X3 



Naples subprovince • Naples 



7 A right valve. X3 



Marcellus shale Chapinville 



8 A right valve. X3 



Naples subprovince Naples 



9, 10 Enlargements of a barite replacement showing the contour of 

 the valve, the width of the flange and the umbonal ridge 

 between the flange and the beak 

 Naples subprovince Honeoye lake 



Pterochaenia fragilis var. orbicularis var. nov. 



[See pi. 4] 

 Page 252 



1 1 A right valve showing the orbicular outline. X2 



Genesee shale Penn Yan 



12 A right valve. X3 



Naples subprovince Naples 



