The British Guiana Museum. 233 
crustaceans and insefts. They are highly organised 
forms, the different systems being well developed. 
Commonly they are termed "shell-fish" — the term beingde- 
rived from the presence of the hard calcareous layer secreted 
by the lining of the outer-fold, or mantle, of the body. 
This shell is all that can be shewn in the dry state. - An 
extremely large number of fossil shells are known, some 
of immense antiquity ; and many of the geological strata 
are recognised by their shells. In the charts on the 
landing will be found illustrations of all the classes of 
molluscs, both recent and fossil forms being given. 
Starting from the coral case, on the left facing the 
door, the visitor sees first the large bivalved or double- 
valved wing-shells (Pinna). The threads by means of 
which these animals adhere to various objects, are very 
long and silky, and have been woven into gloves as 
curiosities. In the following cases, reference will only 
be made to the more special shells, a few out of a large 
number to be seen. In the first case are seen the 
beautiful one-valved volutes (Voluia) among others ; in 
the next follow some very interesting bivalves, such as 
the long razor-shells (Solen), forms that live buried in the 
sand, and the various boring shells, such as Pholas the 
stone-borer, and Teredo a form that bores into wood, 
and thus becoming a pest to sailors and pier-masters ; 
in the next, specimens of different snails, and the 
very curious mail-shells (Chiton) , which are com- 
posed of eight overlapping bands; then follow, in the 
next, the flat-spiral shells of the cuttle-fish group, 
the pearly- nautilus (Nautilus) and the delicate Spirula, 
which is properly an internal chambered shell— 
the paper-nautilus (Argonauta) the commonly-known 
