22 LINN^AN ARRANGEMENT. 



BIVALVES. 



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

 Solen. Hing-e of the shell with the side teeth remote. 

 Tellina. Hinge ofthe shell with lateral teeth of one side wanting. 

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



tratiiig. 

 Mactra. Hinge of the shell with the middle tooth ft)lded. 

 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 obliqne 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 teeth. 

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



no teeth. 



UNIVALVES with a regular spire. 



Argonauta. Shell with one cell ; animal a Sepia. 



Nautilus. Shell with many cells communicating by a small hole. 



Conns. Shell with the aperture efiuse linear, and without teeth. 



