CRABS. 
2 59 
drop, then raising their eyes and peering round, dart hack to the burrow, 
scrape together another heap, and persevere in the same manoeuvre till the 
burrow is of the required depth. It was long supposed that the pincers of 
the male were used as weapons of attack and defence; but, in addition to its 
size, this limb is noticeable for its bright colours, and Mr. Alcock, who observed 
a number of males of an Indian species ( G. annvdipes) waving their large 
claws in the presence of a female, has suggested that their object in so doing 
is to make a display of their gaudy ornamentation and thus influence her choice 
of a mate. 
The third family, Grapsidce, contains species which for the most part are 
shallow-water forms. They are widely distributed, and attract the attention 
of travellers both on account of their bright colours and their extraordinary 
THORNBACK CRAB (3 liat. size). 
activity. Possessing long and powerful legs, tipped with sharp strong claws, 
they are able to dart amongst the rocks on the coast with amazing speed, while 
by means of their flattened carapace and limbs they can slip away into the 
narrowest clefts and chinks. Unlike the majority of the family, the little gulf- 
weed crab (Planes minutus) occurs in temperate and tropical seas, amongst the 
floating weed, and it is said that Columbus adduced its presence as an argument 
in favour of the proximity of land when his sailors were on the verge of mutiny. 
The crabs of the family Pinnotheridce have the carapace soft and membranous 
and the orbits and eye-stalks small. An interesting fact connected with them is 
their habit of living in association with other animals; many species being found 
hiding between the shells of bivalve molluscs, and they have also been discovered 
lodged in the interior of sea-cucumbers. Entering this strange retreat in the zosea 
stage, they never quit it of their own choice. 
In the next tribe, Oxyrhynclia, the carapace is generally narrowed in front 
and wide behind, and furnished between the eyes with a distinct beak, which is 
