LOBSTERS, CRAYFISH, ETC. 



269 



capable of being folded back upon the penultimate. The common shrimp (Crangon 

 vulgaris) occurs in shallow water on sandy coasts of temperate countries of the 

 Northern Hemisphere. Its colour is a speckled grey, corresponding closely with 

 that of the sandy sea-bottom upon which it lives, and in which it buries itself when 

 threatened with danger. To escape the vigilance of fish, shrimps resolutely keep 

 themselves hidden during the day, but come forth at night to hunt for food. The 

 presence of this they perceive by means of scent, since a blind shrimp will find food 

 as quickly as an uninjured one. A second British species is Allman's shrimp 

 (Crangon allmani), abundant in deep water in the Irish Sea and on the west 

 coast of Scotland. It may be at once distinguished by the presence of two fine 

 keels on the upper side of the sixth segment of the abdomen. Both have a short 

 rostrum and no spines on the carapace ; but some of the other members of the 

 family have crests of spines on the carapace, and sometimes a largish rostrum as in 

 the Arctic Sclerocrangon boreas. In Rhynchocinetes typus, from the South Pacific, 



WEST INDIAN PRAWN, Atya (nat. size). 



this rostrum is not only large but movably jointed to the carapace. The section 

 Monocarpinea differs from the last in having the first and second trunk-limbs 

 completely chelate, and the second pair larger than the first. To this section 

 belong a number of fresh- and salt-water forms, and amongst them the Palcemonidce 

 or prawns. The general form of the body is shown in the figure of the common 

 prawn (Leander serratus). In its native haunts the prawn is nearly invisible, 

 being almost colourless, translucent, and marked merely with streaks of various 

 tints. In the rivers of tropical countries occur prawns (Palcemon) rivalling lobsters 

 in size, and remarkable for the length of their pincers, which may exceed that of 

 the body. Among the largest are P. jamaicensis from the West Indies and Central 

 America, and the Indian P. lar, so much esteemed when cooked as a curry. Also 

 belonging to the same section is the family Atyidce, containing a few genera such 

 as Atya and Caridina, found in both Eastern and Western Hemispheres in fresh- 

 water streams and lakes. In Atya the trunk-limbs are curiously constructed, the 

 first two pairs being short and subequal with the two fingers of the pincers tipped 

 with a long tuft of hairs. The remaining three pairs, of which the first is much the 



