38 Beautiful Shells. 
hollow; when the latter, the open end is called the 
Umbilicus, meaning the navel or centre. The 
opening at the bottom, from which the animal 
issues, is the last portion finished, and this is called 
the aperture, a Latin word adopted into the English 
dictionary. Some of these Helices are wide and flat, 
even hollow and cup-like, with the whorls rising 
above the pillar—these are called discoid shells ; 

DISCOID. TURBINATED. 
others which are long and narrow, with projecting 
spires, are termed turbinated shells: the former 
being more or less flat or disk-lke, the latter 
twisted, whirling, like a spinning-top, from the 
Latin twrbo—a whirling, a turning round. 
If we take a Common Snail, and plunge it into 
boiling water, which will instantly kill it, so that 
it can be removed from the shell, we shall find 
the whole of that part of the body which was 
lodged in the upper whorls, or spiral part of the 
shell, is covered with a thin membrane or skin; 
this is called the mantle, and that portion of it 
