286 THE INHABITANTS OF THE SEA. 



larger species are thus able to produce a resistance equivalent 

 to a weight of 150 pounds, which, considering the sharp angle 

 of the shell, is more than sufficient to defy the strength of a 

 man to raise them. They often con- 

 gregate in large numbers in one place, 

 and an old writer compares them to nail- 

 heads struck into the rock. More than a 

 hundred species are known ; one of which, 

 the Patella cochlear of the Cape, is almost 

 invariably found squatting upon the shell of 

 another species of limpet. The finest and largest varieties 

 abound on the shores of the Oriental seas and the coasts of the 

 Mediterranean, but several of the smaller species are very nume- 

 rous in our littoral or sub-littoral zone, where they either feast 

 on the green sea-weeds that we find covering at ebb-tide the 

 stones with a thin emerald layer, or upon the coarser olive- 

 coloured algse. Thus Patella pellucida and Patella lesvis,- 

 both remarkable for longitudinal streaks of iridescent colours 

 on an olive-shell, may generally be found feeding either on 

 the broad fronds or on the roots and stems of the Larninariae,. 

 or Oar-weeds. To their labours may indeed be partly attributed 

 the annual destruction of these gigantic algse, for, eating into- 

 the lower part of the stems, and destroying the branches of the- 

 roots, they so far weaken the base that it is unable to support 

 the weight of the frond, and thus the plant is detached and 

 driven on shore by the waves. 



The beautiful Sea-ear, or Haliotis, is the chief representative 

 of the scutibranchiate gasteropods. The flattened shell, per- 

 forated with small holes on one side, is characterised by a very 

 wide mouth or aperture, the largest in any shell except the 

 limpet. The outside is generally rough, or covered with 

 marine substances; the inside presents the same enamelled 

 appearance as mother-of-pearl, and exhibits the most beautiful 

 colours. The holes with which the shell is perforated serve to 

 admit water to the branchiae, and are formed at regular inter- 

 vals as it increases in size. The foot is very large, having the 

 margin fringed all round, and is able, like that of the chiton 

 or the limpet, to cling firmly to the rock. More than seventy 

 species of Haliotis are known, the greater part occurring in the? 

 Pacific Ocean. 



