Norwich Castle Museum. 119 
which will be seen with other smaller species in the 
collection. The Ship Worm, Zevedo navalts, belongs 
to this destructive family, and there are some fourteen 
species in all. 
British Land, Freshwater, and Marine 
Shells, &c. 
The collection of British Shells has been arranged 
in accordance with the Arztish Conchology of Gwyn 
Jeffreys, which wiil be found to differ considerably 
from that we have been following; it may be that 
some day we shall arrive at something like a uniform 
system, but until that time the student must do his 
best under the circumstances and console himself 
_ with the thought that it is not only in this particular 
branch of Natural Science that the inconvenience 
exists. This want of an uniform system of classifica- 
tion, and the multiplication of synonyms are the 
two greatest stumbling-blocks in the way of the be- 
ginner. 
Mr. Gwyn Jeffreys commences Class I. with the 
Bivalves of the family SpHrip, the first of these is 
the typical genus spherium, Scopoli (Cyclas), the 
members of which are found in ponds and streams, 
burrowing in the mud or floating among the aquatic 
vegetation. S. corneum is a common species, and 
forms a very interesting addition to an aquarium 
where it readily breeds. The members of the genus 
Pisidium (pea-shaped) are much smaller than the pre- 
ceding, but are found in the same localities and their 
habits are similar. 2. amnicum may be taken as a 
type. The Unionip#, or fresh-water mussels, also 
inhabit lakes and running water. They are a well- 
known family, some of them, as U. pictorum—the 
