PLATE XXX. 



Mv i'Ilarca (Plbthomytilus) arenosa. 

 Page i"'3. 



See Plate 87. 

 Fig, l. A right valve of medium size. 



Schoharie pit. Schoharie, N. 1". 



Mytilarca (Plbthi >mytilus) ponderosa. 



i ' : I g I • 251. 



Fig. 2. A right valve of a small specimen. 



Fig. :i. A {•■ft valve of a larger specimen, showing considerable extension of hinge-line. 



Fig. 4. A left valve of medium size. 



Upper Belderberg group. Clarence Hollow, Erie Co., iV T . Y. 

 Fig. ."i. 'I'll.' under side of the rostral portion of a specimen showing the great breadth of tin- striated liga- 

 mental area. The margin of the shell is compressed and bent inwards on the anterior side 

 showing the .surface stria-. 



Upper Helderberg group. Columbus, Ohio. 



Figs. 6, T Th" profile and left views of a large specimen entirely denuded of the test. 



Upper Helderberg group. Columbus, Ohio. 



