CONCHY LI A— BJTHYR J. xlv. 



B. Testce aquarum dulcium. 53—56. 

 Fresh water Shells, 



Independently of their general systematic classification, 

 the fresh water bivalve shells form a series naturally distinct 

 from those of the ocean, by their locality and habits. They 

 have therefore been brought together, as exhibiting a division, the 

 separate study and arrangement'of which may be rendered of 

 more easy and simple accomplishment. 



All the natives of the British Islands have the Ligament 

 external, and are comprehended in four genera, whose essential 

 characters may be thus exemplified 



53. Anodon, Canlo edenhdus, sinu antico marginali. 



Hinge without teeth, with a marginal depression 

 at the anterior side. 



54 Unio, Cardo dentibus primriis, lateralihus nullis. 



Hinge with primary teeth, but no lateral ones. 



35. Mysca, Cardo dentibus juriniariis, lateralibns anticis. 



Hinge with primary teeth, and lateral ones on 

 the anterior side only. 



56, Cyclas. Cardo dentibus duoljus primariis, lateralibns utrinq?(L 

 Hinge with two primary teeth, and lateral onc^^ 

 on each side. 



