Ixxxvi THE VOYAGE OF H.M.S. CHALLENGES. 



and then by dragging the sand over their backs by the aid of their long antennae until 

 they are covered, all but their eyes, which appear above the sand, and suit well the tint 

 of their surroundings. The speckled grey of their surface is common to all the specimens 

 that dwell in shallow water, but often migrants may be found in deeper water, in which 

 the change of colour at first provokes the belief in a distinction of more importance, since 

 with the loss of the speckled appearance they also possess a more slender form, that may 

 be induced through an increase of restless activity in a search for food and from the 

 lessened necessity for hiding from passing dangers. 



On the Japanese coast, in the narrow channels that separate the islands, specimens 

 have been taken at from 10 to 12 fathoms, that so closely resemble our European species 

 that we are not able to determine any constant feature of distinction ; and in fact the 

 Japanese species more closely resemble those of the shallow waters of our bays than do 

 the specimens taken from deeper water in the same locality. 



Not only do we find our common Shrimp, Crangon vulgaris, in the seas of Japan, 

 but we also meet with it on the eastern coast of North America, whilst on the western 

 shores as far south as Mexico there is found a species that Dr. Stimpson named Crangon 

 nigricauda from its having the sixth somite of the pi eon black in colour, but most other 

 observers agree, from a close analytical examination, that it is not distinct from our 

 European species. 



Thus it would appear that this familiar form may be found common perhaps to all 

 the sandy shores of the entire northern hemisphere. 



According to the observation of specimens brought home by the Challenger the several 

 species of Nematocarcinus only differ from one another in the relative length of the 

 projecting rostrum, the numerical value of their dental ornamentation, and the compara- 

 tive length of their legs, which are found to extend over a considerable space. 



The species extend geographically from the line of the southern icy sea-board to 

 the latitude of Japan in the northern hemisphere, and along the line of the Austral- 

 asian Archipelago from Celebes to the Kermadec Islands,- to which I may add that they 

 have been taken in the West Indies by the " Blake " Expedition, and in the Atlantic 

 during the cruise of the " Travailleur." 



In all the habitats recorded, the sea-bottom consists of a Diatomaceous or Globigerina 

 ooze, with the exception of the neighbourhood of the Kermadec Islands, where it is 

 recorded as being rocky, although at a short distance off the island a muddy bottom 

 exists. 



In the track from south to north, that is from the South Indian Ocean, a great line 

 of current has its course over the area occupied by these animals, running up the 

 eastern coast of Australia, and turning westward among the islands of the Archipelago 

 of New Guinea, Celebes, and the Philippine Islands, turning northward and travelling 

 along the eastern shores of Asia, till it sweeps eastward along the shore of Japan. . 



