2 1 2 CRUSTACEA CHAP. 



Talitrus sylcuticiis is very common among fallen leaves and 

 decaying timber in Tasmania and Southern Australia, many 

 miles from the sea, and often at an elevation of several thousand 

 feet. 



Among the Gammaridae, certain genera, e.g. Macrohectopus 

 (Copistantia), from Lake Baikal, are purely fresh -water. An 

 enormous development of Gammaridae was discovered by Dybowsky 

 in Lake Baikal, comprising 116 species, and lately a number more 

 have been found by Korotneff. 1 The majority of these were 

 originally placed in the genus Gammarus, but Stebbing has rightly 

 created a number of peculiar genera for them. Certain species 

 are, however, placed in more widely distributed genera, e.g. Gam- 

 marus and Carinoyoiiniiarus, which is also represented in the 

 Caspian Sea. Korotneff found some remarkable transparent pelagic 

 forms (Constanticb) swimming in the abyssal regions at about 

 600 metres depth, the majority of them being blind, but some 

 possessing rudimentary eyes, often on one side only. 



Besides various species of Gammarus, a number of other 

 Gammaridae are frequently found in brackish water. Among- 

 Haustoriidae Pontoporeia has representatives in both the oceans 

 and inland lakes of the northern hemispheres (see p. 1 3 7). 



Of the Decapoda, seven families are typically fresh-water in 

 habitat the Aegleidae, containing the single species Acylni 

 laevis, related to the Galatheidae, which inhabits streams in 

 temperate S. America, ; the Atyidae, a family of Prawns from 

 the tropical rivers and lakes of the New and Old World, and in 

 the Mediterranean region. A number of Palaemonidae arc- 

 found in fresh water, e.g. Palaemonetes varians in Europe and 

 N. America, while several species of Palaemon occur in lakes, 

 streams, and estuaries of the tropical Old and New World. 



The expeditions of Moore and Cunningtoii to Lake Tan- 

 ganyika brought back an exceedingly rich collection of Prawns, 

 corn prising twelve species, all of which are peculiar to the lake,' 2 

 and tlii.s is all the more surprising since Lakes Nyasa and 

 Victoria Nyan/a arc only known to contain one species, Caridina 

 nilo/ini, \\hich ranges all over Africa and into Queensland and 

 New Caledonia. The Tanganyika species, however, all belong to 

 purely fresh-water genera, and do not afford any suggestion 



1 Arc},. Zool. !:,>!>. i 4), ii., 1904, p. 1. 

 - See Caiman, Proc. Zool. Soc. 1906, p. 187. 



