UNIVALVE MOLLUSCA. 429 
the animal and by that of the shell.  Linnzeus called it Patella, z.c., 
a deep dish or knee-cap. 
The shells of the Patellide are univalve, oval, or circular, non- 
spiral, but terminating in an elliptic cone, concave and simple beneath, 
non-pierced at the summit, entire and inclined anteriorly. They are 
smooth, or ornamented on the sides with ridges radiating from the 
summit, and often covered with scales; the edges are frequently 
dentate. The colours are very varied. The interior is very smooth, 
and remarkable for the brilliancy and lustre of its tints. 
The head of the animal is furnished with two pointed tentacles or 
horns, having an eye at the external base of 
each. The body is oval and nearly circular, 
conical, or depressed. The foot is in the form 
of a thick fleshy disc. Certain lamellar branchiz 
are arranged in series all round the body. 
The limpets dwell upon the sea-shore, in 
the parts alternately covered and uncovered by 
the waves. They are almost always attached 
to rocks, or other submerged bodies, to which 
they adhere with great tenacity. If the com- 
mon limpet (Patella vulgata) is alarmed before 
any attempt is made to dislodge it, no human 
force, pulling in a direct line, can remove it, and 
it can sustain without being crushed a weight of - ane = 
many pounds. It holds on by the great quantity (Deshayes). 
of vertical fibres in its foot, which in raising 
the median part forms in the centre a sort of sucker. It is the 
celebrated experiment of the Magdeburg cups which these little 
molluscs realise by their vital action. 
These animals bury themselves in the chalky rocks to the depth 
of two or three lines; when they are dispersed, they are observed 
constantly to return to the same place. Their movements are, 
besides, extremely slow, the advance of the limpet being only 
perceived by watching the slow upheaval of the shell above the 
plane of its position. It is supposed, from the mouth being armed 
on its upper edge with a large semi-lunar, horny, cutting tooth, and 
in its lower part from having a tongue furnished with horny hooks, 
and from their inhabiting in great numbers places covered with 
marine plants, that their food is chiefly vegetable. 
The poorer inhabitants of the coast eat limpets when they have 
nothing else, but their flesh is singularly coriaceous and indigestible. 
They are found in every sea; but are, however, found to be 
