UNIVALVE MOLLUSC A. 



429 



the animal and by that of the shell. Linnaeus called it Patella, ?>., 

 a deep dish or knee-cap. 



The shells of the Patellidse are univalve, oval, or circular, non- 

 spiral, but temiinating 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 branchice 

 are arranged in series all round the body. 



The limpets dwell upon the sea-shore, in 

 tlie parts alternately covered and uncovered by 

 tlie 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 vitlgata) 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 

 many pounds. It holds on by the great quantity 

 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 posidon. 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 



F ig. 21 u. 



Chiton magnificus 



(Deshayes). 



