OF THE WEALDEN. 
^251 
Unio. Of this freshwater genus Mr. Sowerby 
lias established five species from the specimens 
from Tilgate Forest, which are in my collection ; 
namely, — 
U. aduncus. 
U. antiquus : this is the most common species. 
U- porrectus. 
U. compressiis. 
U. cordiformis. 
Pmmmobia. An elegant little bivalve that is 
of rare occurrence in the cyclas limestone of Bur- 
wash, is referred by Dr. Fleming to this genus : 
it is represented fig. 6. of the woodcut, jiage 218. 
MijtiluH. Shells of this genus were found by 
myself and Mr. Lyell, in a bed of shale, that had 
been washed by a gentle stream which flowed over 
it, and by which many delicate shells were brought 
to view : they are too imperfect to be determined. 
Crustacea. 
Cifpris faha : fig. 7- of woodcut, page 218. 
The Cypris is a crustaceous animal enclosed 
within two valves or shells of an oblong form ; it 
has two anteniiii? terminated by a pencil of hairs ; 
one eye and four legs ; the head concealed, and the 
tail small. It is an inhabitant of fresh water only. 
The two little oblong shells, which appear like the 
two valves of a bivalve, are the only remains of 
this animal that occur in a fossil state, and which 
are profusely distributed throughout the strata of 
the Wealden. It is to the sagacity of Dr. Fitton 
that we are indebted for a knowledge of the va- 
