A SYNOPSIS OF 



14. OSTREA.— Plate 10. 



Animal, a Tethys. 



Shell, bivalve, irregular ; valves uneqvial and somewhat eared. Hinge 



without teeth, but having a strong elastic ligament inserted into a 



hollow in the valves. 



15. ANOMIA.— Plate 11. 



Animal, a Tethys ? 



Shell, bivalve ; fixed, and irregular ; valves unequal, the lower one 

 with a hole at the base, which is stopped by a testaceous plug at 

 the will of the animal. Hinge without teeth, valves united by 

 ligaments. 



16. MYTILUS.— Plate 12. 



Animal, an Ascidia? 



Shell, bivalve, equivalve, fixed by a silky byssus ; the beaks nearly 

 strait, terminal and pointed. Hinge lateral, generally without 

 teeth. Ligament marginal ; muscular impression long and sub- 

 lateral. 



17. PINNA.— Plate 12. 



Animal, a Liraax. 



Shell, bivalve, equivalve, wedge-shaped, gaping at the summit, pointed 

 at the base ; beaks strait. Hinge lateral, without teeth, ligament 

 marginal, linear, and very long. 



18. ARGONAUTA.— Plate 13. 

 Animal, a Clio. 



Shell, univalve, unilocular, involute, boat-shaped; very thin. Spire 

 double-keeled, tuberculated. 



