THE KEYHOLE LIMPET. 11 



FissurellidoB'j its generic name, Fissurella, being 

 derived from the diminutive of fissura, 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 Ibs. 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 ; 



