22 LINN.EAN ARUANGEMENT. 



BIVALVES. 



Mya. Hinge of the shell with a thick hollow tooth. 



Solen. Hinge of the shell with the side teeth remote. 



Tellina. Hingeofthe shell with lateral teethofone sidewanting. 



Cardium. Hinge of the shell witii remote lateral teeth pene- 

 trating. 



Mactra. Hinge of the shell with the middle tooth folded. 



Donax. Hinge of the shell with the remote lateral tooth wanting. 



Venus. Hinge of the shell with approximate diverging teeth. 



Spondylus. Hinge of the shell with two teeth separated by a 

 hollow. 



Chama. Hinge of the shell with two oblique obtuse teeth. 



Area. Hinge of the shell with numerous penetrating teeth. 



Ostrea. Hinge of the shell with an egg-shaped pit, no teeth. 



Anomia. Hinge of the shell with a linear marginal pit, no 

 teeth. 



Mytilus. Hinge of the shell with a distinct awl-shaped pit, 

 no teetli. 



Pinna. Hinge of the shell with one of the margins unitetl, 

 no teeth. 



UNIVALVES with a regular spire. 



Argonauta. Shell with one cell ; animal a Sepia. 



Nautilus. Shell with many cells communicating by a small I»ole. 



Conus. Shell with the aperture efliise linear, and without teeth. 



