The Brachyura (or Crabs) include many species that live in fresh water. Some of these, like the species of _Sesarma_ (see Plate XXIII.) and some other genera of the family Grapsidæ, are common throughout the tropics, passing up the rivers from the brackish water of estuaries, and being often found long distances inland in quite fresh water. The true River Crabs, however, belong to the family Potamonidæ, and are very common throughout the warmer regions of the globe. One species, _Potamon edule_ (Plate XXIII.), formerly called _Telphusa fluviatilis_, is found in the South of Europe (Italy, Greece, etc.). Very numerous species, as yet only imperfectly known, occur throughout the whole of Africa, in Southern Asia, and in the Malay Islands, extending to Australia in the south and Japan on the north. In the New World the River Crabs are found in South America, and extend north to Mexico and the West Indian Islands. Many of the River Crabs are amphibious in habits, and may be found burrowing in marshy ground or in damp forests. The young are hatched from the egg with all the appendages developed, and they remain clinging to the abdomen of the mother until after the first moult, when they are perfectly-formed little Crabs (see Fig. 31, p. 78). [Illustration: _PLATE XXIII_ THE RIVER-CRAB OF SOUTHERN EUROPE, _Potamon edule_ (OR _Telphusa fluviatilis_) (REDUCED) _Sesarma chiragra_, A FRESHWATER CRAB OF FAMILY GRAPSIDÆ. FROM BRAZIL. (SLIGHTLY REDUCED)] The groups which have been mentioned are all characteristic inhabitants of the fresh waters over considerable areas of the surface of the globe. There are, however, in addition to these, certain Crustacea which occur in isolated localities, and have no close allies in fresh waters elsewhere. In the streams of Southern Brazil and Chili there is found a small Crustacean (_Æglea lævis_--Plate XXIV.), not unlike the Galatheas of our own coasts, which is interesting as being the only species of the Anomura found in fresh water. Still more remarkable are the Syncarida, which are represented by two species of "Mountain Shrimps" (see Fig. 84, p. 264) in Tasmania, and by a third species found near Melbourne. These forms have no near allies among living Crustacea, but appear to be related, as will be shown in a later chapter, to certain fossil Crustacea found in Palæozoic rocks. [Illustration: _PLATE XXIV_ _Æglea lævis._ SOUTH AMERICA. (NATURAL SIZE)]