123 The Offictal Guide to the 
but Z navalis is that which causes the greatest 
destruction in this country. The curious little Denta- 
Zium has already been described, p. 116. 
Case ll, 
We now return to the GASTEROPODA, the 
fresh-water section of which we have already described ; 
the first order which presents itself is that of CYCLO- — 
BRANCHIATA, in which the gills are arranged in two 
separate rows, and are covered by the mantle ; this order 
contains the single family Curronip&, known as Chitons. 
They form a very singular group somewhat resembling 
the limpet in structure, but elongated in form, and 
covered by a buckler composed of eight plates fixed 
transversely on the back of the animal. They frequent — 
the line of low water, hiding under stones and sea- 
weed ; Gwyn Jeffreys enumerates ten British species, 
two or three of which are found on our own coast. 
Following the Chitons are the Paretiip”, or Limpets, 
comprising several genera, some of which are’ well- 
known to us. ‘They are largely collected on the rocky 
coasts for bait, and have even been used by the 
poorer classes for food in hard seasons. ‘These in 
turn are succeeded by the Fissure.iipa&, distinguished 
by their cap-shaped shells, having either a slit in front 
or a hole in the centre, hence known as ‘‘ Keyhole” 
Limpets. There are several species, some of which 
are very pretty shells. Capulus hungaricus is an elegant 
shell limpet-like, but the apex turned to the rear, 
somewhat resembling a widely-opened cornucopia. 
Their habits are much the same as those of the 
Limpets. Ca/yftrea is a somewhat similar form of 
shell. The next family is that of Hatiotrp&, the only 
member of which inhabiting our seas is Haliotes tuber- 
culata, the Ormer, or Ear-shell, found abundantly in 
e 
. ‘ 
p 
Saf il 
