MACRURA. 147 



Abdomen little developed, without 

 swimming organs : 



Appendages on the last segment but 

 one ; breast-plate between the bases 

 of the feet partly linear, and partly 

 broad Anomoura. 



Abdomen always bent under the 

 body ; no appendages on the last seg- 

 ment but one ; breast-plate always 

 broad Brachyura. 



Tribe I. Macrura. 



Abdomen large, in general longer than the cara- 

 pace, stretched out, and serving for swimming; 

 always carrying on its under surface thin swim- 

 ming organs (false feet), and furnished at its 

 extremity with swimming plates expanding like 

 a fan. 



External antennas furnished with 

 a large, oval or triangular, moveable 

 plate. 



Antennas inserted in two lines. 



Beak small or wanting ; feet 

 slender ; with appendages at the 

 bases ; abdomen long and com- 

 pressed Peneadce. 



Beak large, compressed and 

 toothed ; feet robust, without ap- 

 pendages Talcemonidce. 



Beak small and flat ; feet robust, 

 without appendages ; first two 

 pairs two-clawed, and one of them 

 often greatly developed . . . Alpheada. 



Antennas inserted in the same 

 line; first pair of feet fanged . . Cmngonida. 



