THE KEYHOLE LIMPET. 11 
Fissurelide; its generic name, fissurella, being 
derived from the diminutive of jisswra, a slit. 
In shape and colour the shell closely resembles 
the ordinary limpet (Patella vulgata), so common 
on our British coasts; possessing a like power 
of adhering to the rocks, with a tenacity requir- 
‘ing knife and hammer to overcome ; its shape is 
conical, the base being occupied by a powerful 
muscle, which is not confined entirely within the 
shell. It performs the office of legs by its ex- 
pansion and contraction, a means by which the 
creature moves from place to place on the rocks; 
a system of progression you may see for your- 
selves, if you watch a garden-snail taking a con- 
stitutional over a cabbage. This muscle also 
enables it to fix itself at pleasure, aided by an 
atmospheric pressure of 15 lbs. to the square 
inch. They browse on seaweed, and are usually 
between tide-marks. 
At the apex of the shell is a hole, somewhat 
oval: hence the name of keyhole. This orifice 
is for the escape of the outgoing branchial cur- 
rent. There are about 120 species, inhabiting 
all parts of the world—India, China, Australia, 
and the Pacific at Vancouver. Island. When 
shell-collecting near Esquimalt Harbour, I fre- 
quently picked up empty fissurellas on the beach ; 
