CRUSTACEA IN RELATION TO MAN 243 



the Lower Danube and in other rivers flowing into 

 the Black Sea sometimes finds its way to the London 

 market, although it is less valued than the red- 

 clawed species. It is distinguished by its long and 

 slender claws, by the spiny edges of the rostrum, and 

 by other characters. A fourth species (A . torrentium), 

 occurring chiefly in Central Europe, is very closely 

 allied to A.pallipes, and, Hke it, is of little value for 

 the table. 



Within the last thirty years the Crayfish fisheries 

 of Western Europe have suffered heavily from out- 

 breaks of an epidemic disease which has all but 

 exterminated these animals in certain districts. 

 In this country it is said to be responsible for the 

 almost complete disappearance of Crayfish from 

 localities where they were formerly plentiful, as, for 

 instance, in the neighbourhood of Oxford. The 

 cause of the disease is believed to be a protozoan 

 parasite belonging to the group Myxosporidia. 



In other parts of the world it does not seem that 

 the fresh-water Crayfishes are of much importance 

 as an article of food. Some species of Cambavus are 

 so used to a Hmited extent in the United States, and 

 the gigantic Astacopsis serratus (Plate XX.) is known 

 as the " Murray River Lobster " in the markets 

 of Sydney and Melbourne. 



The Decapods of the suborder Natantia comprise 

 a large number of edible species, generally known 

 as Shrimps and Prawns. The Common Shrimp, 



