23 



entirely in fresh water, wliile a considerable numljer are amphibious, and not a 

 few live entirely on land, only visiting the sea periodically. 



The marine crabs are found everywhere, but are most numerous in wnrm 

 seas. Most of them are inhabitants of the littoral and shallow water, but the 

 moderate depths up to 50 fathoms are also rich in species. A fair number of 

 species are found in -50-100 fathoms, while the depths between 100 and 500 

 fathoms are by no means poor in crabs. Below 1000 fathoms, however, crabs 

 are not met with in abundance, although a species of Etlium. w^as dredged h\ 

 the " Challengel- " at the enormous depth of 1875 fathoms. In these seas the 

 greatest depth at which a crab {Ethusa investigator is) has been found is loOO 

 fathoms. 



I^he habits of the littoral and shallow-water species are extremely variable. 

 Many species shelter in the rocks and reefs, and some burrow in sand and shingle 

 and mud. Many sluggish and inoffensive species are curiously coloured and 

 sculptured so as to resemble the broken shells and bits of eroded and incrusted 

 coi-al-rock among which they live, while other such species actually deck them- 

 selves mth a patchwork of pieces of seaweed and fragments of shell so as to 

 escape notice. Numerovis small species pass their lives esconced among the 

 bi'anches of living zoophyte-colonies, or among the spines of Echinoderms, and 

 are coloured exactly like their hosts. Many Bromiidas carry about a hoijse of 

 their ovm., in the form of a sponge which fits tightly over their carapace ; whih' 

 other species of this family, and of the Borlppida', roof themselves over "with the 

 dead valve of a Lamellibranch shell, upon which it is common to find a sea- 

 anemone growing. Other small species (notably among the T'innoteridse) live as 

 commensals in the mantle-chamber of living bivalve moUusks, or in the cloaca of 

 Holothurians, or in the tubes of Annelids, or in the atrial cavity of Asgidians. 

 Some bold and active species, such as the Grapsi, expose themselves fearlessly 

 on the rocks between tide-marks, trusting to their speed and craft to escape 

 their enemies ; while other active species, such as the PortunidsB and Matididx, 

 have their legs modified to form paddles by means of Avhich they swim with 

 much ease and speed. A few species {Plagvsia, Planes, Yaruna) make their 

 home on drift timber, drift seaweed, hulls of ships, etc., and so may be regarded 

 as belonging to the oceanic fauna. 



The majority of freshimin- crabs belong to the CycloniGtope family of 

 Telplmsidx, although there are numerous Catometopes that also live in fresh- 

 water. During the hot and dry season some of these are accustomed to aestivate, 

 burrowing deep into the moister layers of the soil. 



The ampldbions crabs are for the most jjart Catometopes. They are 

 generally gregarious and live close to the seashore, or among estuarine swamps, 

 in biirrows. They obtain their food along shore, and can breathe air so long as 

 their gill-chambers are kept moist. Although their burrows are usually flooded 



