2236 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- 
pp Steen 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 shel! 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 alge. Thus Patella pellucida and Patella levis, 
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 Laminarie, 
or Oar-weeds. To their labours may indeed be partly attributed 
the annual destruction of these gigantic alge, 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 branchiz, 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. 
Limpet and Shell. 
