226 SYSTEMATIC ZOOLOGY. 



(p. 221) is usually passed in the egg. Besides several 

 unimportant groups, this subclass contains the orders 

 Decapoda and Tetradecapoda. 



ORDER I. 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 they all 

 have eyes on movable stalks, the anterior part of the 

 body or cephalothorax (thirteen segments) is covered by 

 a fold of the integument known as the carapax, and the 

 gills are (usually) borne packed away in a pair of gill- 

 chambers beneath the carapax above the walking-legs. 



This group of Decapoda is subdivided into three sub- 

 orders, according among other things, to the characters 

 presented by the abdomen. In the MACRURA 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 intermediate 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 a few points, 

 except size, from the fresh- water crayfish. These play 

 a great part in the food-supply of northern Europe and 

 the eastern 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 



