No. 26.] ARTHROSTRACA OF CONNECTICUT. 49 



LL. Thoracic segments not strongly tuber- 



culated. 



M. Postero-lateral margin of third ab- 

 dominal segment serrated 



Apherusa. 



MM. Postero-lateral margin produced to 

 a single tooth, above which is a 

 small sinus. 



N. Uropod 3 biramous Sympleustes p. 84 

 NN. Uropod 3 uniramous ..Unciola p. 165 

 MMM. Postero-lateral margin otherwise; 

 accessory flagellum present; uro- 

 pod 3 flattened and usually project- 

 ing beyond the others; gnathopods 

 subchelate, gnathopod 2 larger 

 than i and larger in male than fe- 

 male; telson small and flattened 

 (Gammaridae). 



N. Uropod 3 uniramous Crangonyx p. 95 

 NN. Uropod 3 biramous. 



O. Telson slightly emarginate 



Eucrangonyx p. 93 

 OO. Telson deeply cleft. 



P. Inner ramus of uropod 3 rudi- 

 mentary, scale-like Melita p. 98 

 PP. Inner ramus of uropod 3 often 

 smaller than outer, but not 

 rudimentary. 

 Q. Last 3 abdominal segments 



with fascicles of spines. 

 R. Body with median carina.. 



Carinogammarus p. 113 

 RR. Abdominal segments 4 

 and 5 raised dorsally to 

 spiniferous tubercles . . . 



Dikerogammarus p. 105 

 RRR. Body without carina or 



tubercles Gammarus p. 107 

 QQ. Last 3 abdominal segments 

 without fascicles of spines; 

 uropod 3 with compara- 

 tively broad, short rami . . 



Elasmopus p. 102 

 KK. Mandible with palp; uropods 2 and 3 



enormously developed Chelura p. 174 



KKK. Mandible without palp; no accessory 

 flagellum; uropods 2 and 3 normal. 



