Classification of the Decapod Crustaceans. 481 



Chelipt'da much bigger tlmn the other legs. 

 Branchial regions of the body deeply sepa- 



ratetl I'loni cardiac Parthenopina;. 



II. Carapace usually sharply pentagonal. Ros- 

 trum cleft into two. Chelipeds of moderate 

 size. Branchial regions of the body not 

 deeply separated from cardiac Eumedonince. 



Key to the Families of the Bracliyiliyncha. 



I, Orbits formed, but more or less incomplete. 



Second antennal flagella, when present, 



long and hairy. Rostrum present. Body 



elongate-oval. Fore edge of the mouth 



indistinct Corystidae. 



II. Orbits complete (though fissures may remain), 



except in the Mictyrinfe, where the ej^es are 



almost or quite unprotected. Body rarely 



elongate-oval. Rostrum often wanting. 



Second antennal tlagi;lla usually short, not 



hairy. 

 A. Carpopodites of third maxillipeds articu- 

 late at or near antero-internal angle of 

 the meropodites. Body usually round or 

 transversely oval. Male openings nearly 

 always coxal. In many species the right 

 chela is always larger than the loft. 



1. Legs more or less distinctly adapted for 



swimming. Usually a small lobe on the 

 inner angle of the endopodite in the first 

 maxillipeds. [First antennte foldslanting 

 or transverse. J Portunidae. 



2. Legs not adapted for swimming, or, if so 



moditied, then the vas deferens opens 

 sternally or runs in a sternal groove 

 (certain Macrophthalmus and Lihystes). 

 Inner lobe on the endopodite in the first 

 maxillipeds wanting. 



a. Freshwater crabs with the branchial 



region much developed and swollen. 

 [Body often squarish, but male open- 

 ing coxal.] Potamonidae. 



b. Marine crabs, with the branchial region 



not greatly swollen. 

 i. First antennse fold lengthwise. 



(«) Carapace subcircular. Second 

 antennal flagella either long and 

 hairy or wanting Atelecyclidae *. 



(6) Carapace broadly oval or hexa- 

 gonal. Second antennal flagella 

 present, short, not hairy Cstncridae. 



* Tn'chia, de llaan, is somewhere in Iho neighbourhood of this 

 family. 



