PLATE 79. 



Fig. 1, 2. 706, 4. Pentamerus occidentalis. (Pag- 341.) 



1 a. Cast of the dorsal valve of a young specimen, preserving the shell towards the base. 



1 b. Interior of the preceding, showing the elongated beak and foramen. 



1 c. Profile view of a young specimen, the shell being nearly all removed. 



1 d. Dorsal valve of the preceding specimen. 



1 c. Cast of the dorsal valve of a small specimen, showing the original tliickness of the shell at the beak 



from the extension of the central plate. 

 1 /. Cast of the dorsal valve of a larger specimen. 

 1 g tf k. Ventral valves having the shell partially preserved. 



1 i. Profile view of a ventricose specimen, the beak of the dorsal valve being reduced by abrasion. 

 1 k. Cardinal view of the largest individual seen, showing the numerous lamina; of which the thick shell is 



composed at the beak. 

 1 /. Profile view of the same. 



1 m. Cast of the dorsal valve, having the beaks little extended. 

 1 0. A cast of the dorsal valve, the two sides separated more than usual. 

 1 p. The interior of the dorsal valve, where the outer lamina; of the central plate have become separated by 



the removal of the inner ones, giving the appearance of two plates. 

 1 r. The interior of a dorsal valve, showing the separated lamina; of the internal plate near the beak. 

 1 s. Cardinal view of an imperfect specimen, the ventral valve showing the two plates extending fiom near 



the beak downwards. 

 2. The interior of a small dorsal valve, perhaps a distinct species. 



