256 
CRUSTACEANS. 
characterised by having the carapace much wider than long. As an article of 
food the male is more esteemed than the female, being larger and having larger 
claws. The two sexes, as in all crabs, may be distinguished by the size of the 
tails, this organ in the male being narrower, more pointed, and having fewer and 
smaller appendages than in the 
female. The family Cancridce 
is represented in tropical seas 
by a large number of species 
and genera, some of which, such 
as Actcea, have the carapaco 
covered with granules, and 
ornamented with a network of 
deep grooves. 
The members of the family 
Portunidce may be recognised 
by a modification of the last 
pair of legs. In the great 
young edible crab. majority of crabs these legs are 
like the rest, ending with a 
long, slender - pointed foot, which bears evidence to its being an organ for 
running, climbing, or crawling; but in the Portunidce these legs are much 
flattened, the last segment in particular being dilated into an oval plate. The 
creatures are thus equipped with a pair of oars, by means of which they swim 
Several species of the typical genus Portunus are found in British waters, and 
many of them are hand¬ 
somely coloured, although 
none are such expert 
swimmers as the tropical 
species, especially those 
inhabiting the gulf-weed 
of the Atlantic. The 
peculiar motion of the 
oar-like feet has given 
rise to the name of 
fiddler - crabs, so often 
applied to the group. 
The figured species 
(Thalamita natator ) is a 
native of the tiopical swimming-crab (nat. size), 
seas. The common British 
shore or green crab ( Carcinus mcenas), which is referred to this family, differs 
from the rest in having the legs of the last pair adapted for walking, being armed 
with a claw, and not flattened into a paddle. Connecting the present with the 
following section, is the family Thelphusidce, which contains a number of genera 
and species found in fresh-water streams, or on land, and sometimes ascending 
mountains, in temperate and tropical regions. One of the best known species is 
