54 
water formation on the Isle of Wight, by Prof. Sedg- 
wick ; it is accompanied with Melaneae fasciata and 
costata t. 241, Lymneae, and other shells. 
Should the genus Potamides, to which the above 
species are referred, continue to be received by Concho- 
logists, it is likely that many, if not the greater part of 
Lamarck’s 60 fossil Cerites will be referred to it ; for as 
there are very few in the London Clay in England, it 
is probable that most of the species he has described 
belong either to the acknowledged fresh water formations, 
or to the doubtful or mixed strata known by the name of 
Plastic Clay, or upper marine formations, such as those 
of Woolwich, Newhaven, the Isle of Wight, the neigh- 
bourhood of Paris, & c. 
