118 On the Land and Fresh Water Mollusca of Great Britain. 



2. Cellensis, Pf. 



3. Intermedins, Lam. 



4. Anatinus, Lam. 



5. Ventricosus, Pf. 



Gen. 28. Unio, Bruguiere. 

 1. Margaritiferus, Lin. Nils. 

 9. Tumidus, Nils. 



Mysca solida, Turt. 

 ovata, Turt. 



3. Pictorurn, Linn. Lam. 



4. Roslratns, Lam. 



5. Bataviis, Lam. 



The foregoing is given as the nearest approximation to a correct 

 list of the British species of Anodon and Unio (according to the 

 views of Pfeiffer) which the present state of our knowledge will 

 allow ; but so various are the opinions of authors on thesf* difficult 

 genera, and so little have the British species been investigated, that 

 we are much in need of further information on the subject. 



Fam. Cycladje, Flem. (Les Cyclades, Fer.) 

 Gen. 29. Cyclas, Bruguiere. 



1. Rivicola, Leach. 



2. Cornea, Linn., Lam. 



3. Calyculata, Drap. 



Var. C. lacustris, Turt. Aid. 

 The Cyclas lacustris of Draparnaud is certainly unknown to Bri- 

 tish naturalists ; but as the species is described by most of the con- 

 tinental authors, we might naturally conclude that they were well 

 acquainted with it. The contrary, however, appears to be the fact. 

 M. de Ferussac, who, from his extensive correspondence, might 

 have been expected to possess the best information on the subject, 

 gave me a variety of C. cornea (frequently found in this country) as 

 the supposed C. lacustris, Drap. This, though slightly rhomboidal 

 in outline, does not agree very well with Draparnaud's description. 

 Mr Clark has a shell obtained in Devonshire which comes nearer to 

 it. It is to be hoped that this gentleman will shortly lay before 

 the public the store of very valuable information on British Mol- 

 luscous animals of which he is possessed. 



Gen. 30. Pisidium, Pfeiffer. 

 1. Obtusale,J?i.} Jen. 



