PLATK XXX. 



Mviir.AUCA (Pl,KTIl()MVTILUs) AltKXO.SA. 



I'age -i-i;). 



Sop Plate 87. 

 Kit.'. 1. .\ lif^ht viilvH of niydium si/o. 



Schoharie g-i-it, f^alioliarie, N. Y. 



MVTILAUCA (Pl.ETHOMYTILUS) PONDEKOSA. 

 Viigc *2.>4. 

 KifT. 2. A lifrht valve of a small specimen. 



Ki);. '.i. A. left valve of a lavijer specimen, showing' con-siderable extension of hinge-line. 

 Fiir. 4. A left valve of meilium .size. 



Upper HelrlcM-lierg group. Clarence. Hollow. Erie Co., N. Y. 

 Fig. 5. The under .side of the rosti-al portion of a specimen showing the gi-eat breadth of the striated liga- 

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

 showing the surface striiE. 



Upper Helderberg group. Columbus, Ohio. 



Figs, li, 7. The profile and left \iews of a large specimen entirely denuded of the te.8t. 



Upper Helderberg group. Columbus, Ohio. 



