164 DESCRIPTION OF SHELLS. 
Time and circumstances have in most instances destroyed in fossil shells the 
membranous portion, and with it their colour and nacrous character ; but there 
can be no doubt that many of them were as beautiful as those of the present day. 
The Cones and Cowries might vie with the most splendid recent species, the 
Tellens and other bivalves, in the delicate painting of their fabric; and the 
Nautili with the finest examples from tropical regions. I have seen in a few 
instances, more especially on the Cones and Tellens from Bracklesham, slight 
traces of their original colour. 
Shells are univalve, bivalve, or multivalve, according as they consist of one, 
two or more pieces. Univalve shells have generally a spiral form ; some Mol- 
lusca have internal shells for the defence and support of particular organs. 
The fossil shells of Selsey and Bracklesham, owing to their constant exposure 
to the sea-water, are soft and require much care; they are often perforated by 
parasitic worms. At Barton the Volutes in particular, which come under the 
class denominated porcellaneous, are very hard and oftentimes transparent, the 
lime being replaced by silex. 
CONCHIFERA DIMYARIA. 
Clavagella coronata. (Tab. II. fig. 17 & 19.) 
The specimens are small and extremely tender ; they retain their pearly lustre. 
The form of the tube is very variable. 
Gastrochena Corallium. (Tab. II. fig. 27.) 
Spec. Cuar.—Broad ovate, anterior extremity small, truncated, terminating 
in a point. 
This is a broader-formed shell than most of its congeners, and less curved, 
but the opening for the foot is nevertheless very large and is terminated an- 
teriorly by a sharp angle. 
A very frequent inhabitant of Siderastrea Websteri, boring it in all directions ; 
it is so thin and tender that it is very seldom perfect specimens can be extracted 
from the holes, which are generally filled with sandy and ferruginous clay. 
Panopea corrugata. (Tab. If. fig. 12.) 
Spec. Cuar.—Transversely ovate-elongated, nearly cylindrical, rather com- 
