DECAPODA. 



Those forms which are commonly known as crayfish, 

 shrimps, lobsters, prawns, and crabs are collectively known 

 as Decapods, from the fact that, including the large claws, 

 they have ten walking-feet. Besides this we find that they 

 all have eyes on movable stalks, the anterior part of the 

 body (thirteen segments) is covered by a fold of the integu- 

 ment known as the carapax, and the gills are (usually) 

 borne packed away in a gill-chamber above the walking- 

 legs. 



This group of Decapoda is subdivided into three divisions, 

 or " suborders," according, among other things, to the 

 characters presented by the abdomen. In the MAGRURA 

 it is, as shown in the crayfish, very large, and is carried 

 well extended; in the BRACHYURA it is much smaller, 

 not nearly so large as the cephalothorax, and is folded up 

 beneath the latter region so that it is not visible from above. 

 In the third group, the ANOMURA, the abdomen is inter- 

 mediate between the conditions found in the other groups, 

 and frequently it is much softer than the other regions. 



Of the Macrura the most important are the lobsters, 

 which are large marine forms differing in few points, except 

 size, from the fresh-water crayfish. These play a great 

 part in the food-supply of northern Europe and the east- 

 ern United States. They are mostly captured by sinking 

 large wooden traps (lobster-pots) baited with refuse fish, 

 and at intervals hauling up the pots. The number thus 



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