PLATE 79. 
1, 2. 706. 4. Pentamertts 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 e. Cast of the dorsal valve of a small specimen, showing the original thickness of the shell at the beak 
from the extension of the central plate. 
1 f. Cast of the dorsal valve of a larger specimen. 
1 g Sf h. Ventral valveshaving 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 laminae of which the thick shell is 
composed at the beak. 
1 l. Profile view of the same. 
1 m. Cast of the dorsal valve, having the beaks little extended. 
1 o. A cast of the dorsal valve, the two sides separated more than usual. 
1 p. The interior of the dorsal valve, where the outer laminae 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 laminae of the internal plate near the beak. 
1 s. Cardinal view of an imperfect specimen, the ventral valve showing the two plates extending from near 
the beak downwards. 
2. The interior of a small dorsal valve, perhaps a distinct species. 
