ROOM III. FAUNA AND FLORA OF THE WEALDEN. 219 



mind to the fluviatile nature of those deposits, and assisted 

 in establishing the fresh-water origin of the entire series now 

 comprised in that formation. 



The shells of the Wealden. as might be anticipated from the 

 character of the molluscous fauna of the rivers and lakes of 

 the present time, though occurring in immense numbers in 

 some of the beds, comprise but an inconsiderable number of 

 genera ; and these, with but few exceptions, are fluviatile, or 

 lacustrine forms : no traces of land mollusks have, I believe, 

 been observed. 



The species hitherto met with in this country belong to 

 the genera Paludina, Limnea, Physa, Planorbis, Paludina, 

 Melania, and Cyclas, Cyrena, Psammobia, Unio, Mytilus, &c. ; 

 brackish water and marine shells occasionally occur in some 

 of the lower deposits ; and in the Purbeck series there is 

 a bed of oyster shells. The most remarkable fact relating 

 to the fresh- water mollusca is the discovery by that eminent 

 naturalist Prof. Edward Forbes, in the Purbeck strata, of 

 shells, of the genera Physa, Planorbis, and Limnea, that 

 closely resemble the existing species inhabiting our pools and 

 rivers. 



In my first published account of the fossils of Tilgate 

 Forest, a few species of paludina, and of unio and cyclas 

 and cyrena, comprised all the mollusks then known. The 

 Sussex or Petworth shelly limestone, some layers of which 

 take a good polish, and are, therefore, called marble, is a 

 mass of paludinaa of two or three species, with innume- 

 rable cases or shells of the fresh-water entomostracous 

 crustaceans, Cypris and Estheria ; and some of the bands 

 of limestone almost wholly consist of a small species of unio. 



Some of the beds of cky abound in potamides and melaniae, 

 and others are made up of the shells of the fresh-water bivalves 

 cyrena and cyclas. The most remarkable and interesting of 

 these fluviatile mollusks, are the large mussels (Unio Val- 

 densis) first discovered by me in the Tsle of Wight, and 

 which equal in size, and closely resemble in form, some ex- 

 isting species that inhabit the Ohio and Mississippi. 1 



Insects. A few legs and elytra of Insects have been found 

 in the Wealden of Kent, and a considerable number of 



1 See "Geological Excursions round the Isle of Wight." PL VI. 



