8 
Marine shellfish live in all kinds of places below high water 
mark; and some of the semi-amphibious ones thrive even above 
ordinary high water mark, where for days at a time nothing but 
the tops of the waves could reach them. They are found on sea- 
weed and on rocks, and on sand or mud-banks; but especially in 
places near rocks on marine grass banks bare at low spring tides. 
Some live on the surface of the water, some burrow in sand or mud, 
and some bore holes for themselves in the softer rocks. Some live 
in deep water; but the better coloured shells are found near low 
water mark, or in shallow water; for light is as necessary to the 
perfecting of colour in shells as in flowers. Shells that have grown 
in a harbour are more fragile than those grown in the ocean, and 
are usually less brilliant in colour, as harbour water is not as 
clean as ocean water. The colour of shells (as of insects) depends 
largely on environment, and is only one, and by no means the 
most reliable, method of deciding the species. An expert can at 
a glance tell whether a given shell has come from shallow or deep 
water, and whether from an exposed or sheltered spot. Most shell- 
fish move about a great deal, and migrate into deeper water in 
summer ; and on bright clear days retire into dark corners amongst, 
and even under, stones. On a dull day a collector is frequently 
more successful than on a bright, sunny day; and in spring or 
early summer the best hauls of live shells can be made. Nearly 
all shells have an epidermis, or outer skin. In some this is very 
apparent, as in the Lotorium olearium (Plate V., Fig. 1), or the 
Solenomya parkinsoni (Plate IX, Fig. 18), while in others it is 
nearly transparent, and hardly perceptible. To enable the true 
colours of a shell to be seen the epidermis must be removed. 
The supposed original form of a shell was that of a volute 
univalve, such as the Triton (now Lotorium), or Struthiolaria. To 
properly enclose the animal, and make it safe from enemies, an 
operculum, or lid, was so formed that when the animal retired 
into the shell this filled up the opening. The operculum is 
usually like a piece of thin, rough brown horn, and where no 
reference is made to an operculum in this work, it must be under- 
stood that the operculum is horny. Some shells, such as the As- 
tralium suleatum (Plate VI., Fig. 18), and the Turbo helicinus 
(Plate VI., Fig. 17), have a shelly operculum; that of the latter 
being the well-known cat’s eye. 
In some shells the operculum is small, in others large, and 
progressing step by step we find some, such as the scallop and oyster, 
