MOLLUSCS: = - - seal 
MARINE MoLuuscs. 
Although land molluscs are by no means uncommon, 
it 1s the marine forms which are most plentiful and 
best known. They occur everywhere along our coasts, 
and in certain special localities are found in great 
numbers and variety. It is in the study of marine shells 
that children will probably display most interest, and 
it is by means of these that they will most readily grasp 
the idea of the two main divisions of molluscs—univalves 
and bivalves. 
Univalves. Beginning with the univalves, a good 
form to study is turbo, found in considerable numbers 
along rocky or boulder-strewn coasts. In size the shell 
varies a good deal, 
some of the larger 
specimens being up- 
wards of two inches 
in height. In colour 
the shell is almost 
black, but after being 
kept for some time it 
changes to a reddish 
brown. It consists 
of a large body- 
whorl, and a rela- 
tively short spire. 
Fig. 73.—Turbo Smaragdus. The mouth of the 
shell is circular, and 
the lip whole or entire. When disturbed the animal 
withdraws into its shell, the mouth of which is closed by 
a solid calcareous plate (the operculum or gill-cover) 
attached to the extremity of the foot. The operculum 
is smooth, bright green in colour, and, being easily polished, 
is sometimes used in making ornaments of various kinds, 
