74 
Guide to Crustacea. 
Table-case are almost entirely terrestrial in habits. The carapace is more or 
No. 16. j egs transversely oval, and the front is of moderate breadth. The 
branchial regions of the carapace are generally swollen, and the 
lining membrane of the gill-chamber is richly supplied with blood- 
vessels, and acts as a lung. Typical genera are Geocarcinus, Car- 
clisoma, and Uca. 
The Crabs of the family Grapsidae are the most typical Cato- 
metopa. The carapace is nearly quadrilateral, with the front very 
broad, and the orbits near the antero-lateral corners. Many 
species are estuarine or fluviatile in habitat. The species of 
Grapsus and allied genera are common shore Crabs in all the 
warmer seas. 
The genus Sesarma and its allies include, for the most part, 
amphibious fresh- water Crabs, abundant in the tropical regions of 
the Old and New Worlds. 
Varuna litter ata is widely distributed throughout the Indo- 
Pacific region, and seems to be equally at home in freshwater and 
in the sea. It is often found clinging to drift-wood at the surface 
of the sea. 
The little Planes minutus also lives at the surface of the open 
sea, clinging to floating weed or drift-wood, or to the bodies of 
large marine animals such as turtles. It is especially abundant 
in the Sargasso Sea, but is widely distributed in the warmer regions 
of all the oceans, and is occasionally carried to the South and West 
coasts of the British Islands. It is related of this species that 
“ Columbus, finding this alive on the Sargasso floating in the sea, 
conceived himself not far from some land, on the first voyage he 
made on the discovery of the West Indies ” (Sloane, Nat. Hist. 
Jamaica, ii. p. 2). 
In the family Ocypodidae the front is generally narrow and the 
eye-stalks are often very long. Most of the species are amphibious 
shore Crabs, burrowing and often gregarious in their habits. 
Several species of the typical genus Ocypoda are exhibited. 
The species of Gelasimus, often called “Fiddler Crabs” or 
“ Calling Crabs,” are common on most tropical shores, living in 
vast numbers in salt marshes or between tide-marks, where they 
make burrows in the sand or mud. A group of specimens of two 
species is mounted in Wall-case No. 5. The genus is of interest 
as exhibiting in an extreme degree two characters which are more 
or less marked in nearly all Crabs — the unequal development of 
the chelae or pincers on the two sides of the body, and their 
greater size in the male sex. The large, brightly coloured claws 
