FOSSIL FRESH-WATER UNIVALVES. 423 
country inhabited by the Iguanodon and other colossal 
reptiles, all of which have long since become extinct. With 
the exception of the mussel-band limestone of the Carboni- 
ferous system, previously described, these are the only British 
fresh-water marbles.* There are four species of Paludina 
in the Wealden, and four in the Tertiary strata of Hants. 
Liwvza. Lign. 133, fig. 2.—Several species of these 
fresh-water mollusks inhabit our lakes and ponds, and may 
be known by their pointed spire, elongated oval body, and 
delicate thin shell; on the inner lip of the aperture there is 
an oblique fold. Fossil shells of this genus are found with 
Paludinee in the fresh-water tertiary deposits. Headon 
Hill and other localities in the Isle of Wight abound in 
these shells; and in the limestone of Calbourn beautiful 
casts are very numerous. The Paris basin yields several 
species ; and there are six species in the Isle of Wight 
Tertiary ; I have not observed any decided examples in the 
Wealden. In the sands and clays the shells are well pre- 
served; in the limestones the casts only remain. Shells of 
another genus of fresh-water spiral univalves, termed Bult- 
mus (Ly. p. 30), are found associated with the above. A 
large species (B. ellipticus, Min. Conch, tab. 337), occurs 
in the limestone at Binstead, near Ryde, and at Calbourn; 
I have collected specimens two inches long from the former 
locality ; they are generally in the state of casts, with a 
white friable coating of the shell.t 
Pranorsis. Ly. p. 29. Wond. p.400.— The shells of 
this genus are also numerous in our rivers and lakes, and 
* The collector may obtain specimens, and polished slabs of these 
limestones, of Mr. Martin, mason, Lewes, Sussex. 
+ A very large species of Limncea from Bavaria (labelled L. 
maxima) is in the British Museum. It is a cast six and a half inches 
long, and is placed with the recent shells. Prof. E. Forbes has dis- 
covered a Limneid (Physa) in the Purbeck strata. 
