Tribe Gammaridea. 



Head rather small, not fused with first thoracic segment ; e3'es 

 rarely of very large. size, usually compound, first antennae consisting 

 of 3-jointed peduncle and flagellum ; second antennae with peduncle 

 usually consisting of 5 joints and flagellum ; maxillipeds with inner 

 plates free and with 2- to 4-jointed palps. 



Body usually compressed; thorax of 7 distinct segments, rarely 

 reduced to 6 ; 5 or 6 segments bearing gills ; 4 segments in female 

 bearing marsupial plates; thoracic legs overlapped at base by epi- 

 mera, the first 4 being usually larger than the posterior 3. 



First 3 abdominal segments always free ; posterior 3 usually dis- 

 tinct ; uropod 1 always biramous. 



Key to the genera of the Gammaridea. 



I Guathojjod 2 with tliuxl joint elongate .... Lysiauassa 

 I Gnathopod 2 with third joint short .... 2 



IGnathopod 2 with fifth joint greatly prolonged ; 

 telson elongate, tapering, entire Amphilochus 

 Not with same combination of characters . . 3 

 IGnathopod 1 with chela formed bj^ fifth and sixth 

 joints Leucothoe 

 Gnathoj)od 1 otherwise 4 



Epimeron 4 enormously developed Stenothoe 



Epimeron 4 not especially large 6 



Gnathopods 1 and 2 simple ; body depressed and 

 ridged dorsally ; pleopod 3 with j)eduncle ex- 

 panded to form long process Pariphinotus 



Not with same combination of characters . . G 



Gnathopod 2 with second joint rather slender and 



greatlj^ enlarged distally, gnathopod 1 ver3' 



small Colomastix 



Gnathopods otherwise 7 



Epimera 1—3 tapering acutely ventrally .... Fanoploeopsis 

 Epimera 1—3 more or less rounded ventrally . 8 



Antennae with calceoli 9 



Antennae without calceoli 10 



