PLATE XX. 



Page. 



Pinna pktrixa White &8 



Fig. 1. Left valve of the type specimen. (See PI. xix, Fig. 4.) 

 Nat. Mus. Cat. Invert. Foss., 8640. 

 Tiugonarca obliqua Meek 92 



Nat. Mus. Cat. Invert. Foss. ; 22869. 

 Fig. 2. Hinge of right valve. 



3. Dorsal view of a small specimen. 



4. Posterior view of a larger example with shell removed from left valve, 



showing the imprint of the ridge that borders the muscular scar. 



5. Left side view of the same specimen. 



6. Left valve of a large specimen. (See Fig. 1 on PI. xix.) 



232 



