242 U.S. NATIONAL MUSEUM BULLETIN 271 



normal; uropod 3 short, not exceeding uropod 1, rami not longer 

 than peduncle, outer 1-articulate, inner slightly shortened; telson 

 cleft; urosome dorsally carinate; palm and posterior margin oj article 

 6 on gnathopod 2 not sejMrate, article 7 nearly as long as article 6 (com- 

 bination of characters). Species: 1, subtropical E. Atlantic and 

 Mediterranean, littoral. 



Garnmarellus Herbsl 



Gammarellus Herbst, 1793. — Stebbing, 1906. 



Amathia Rathke, 1837 (homonvm, Hydrozoa). 



Grayia Bate, 1862.— Bate and Wcstwood, 1863. 



AmathiUa Bate and Westwood, 1863 (new name for Amathia). 



Type-species: Astacus homari J. C. Fabricius, 1779 (type indicated 

 by Stebbing, 1899a, but firmly selected by Chevreux and Fage, 

 1925). See Sars, 1895. 



Accessory flagellum more than 3-articulate ; lower lip lacking inner 

 lobes; inner plates of maxillae 1-2 densely setose medially; gnathopods 

 normal; uropod 3 short, not exceeding uropod 1, rami lanceolate, 

 outer 1-articulate; telson entire or emarginate; body dorsally carinate. 

 Species: 2, arctic and high boreal, littoral. 



Gamrnarus Fabricius 



Gammarus Fabricius, 1775. — Stebbing, 1906. 



Marinogammarus Schellenberg, 1937a — Sexton and Spooner, 1940 [subgenus, 



often considered a full genus]. 

 Pectenogammarus Reid, 1940 [valid subgenus]. 



Type-species: Cancer locusta Linne, 1758 (selected by Boeck, 1876). 

 See Sars, 1895. 



Accessory flagellum 3- or more articulate; lower lip with inner 

 lobes obsolescent or absent; inner plates of maxillae 1-2 densely 

 setose medially; gnathopods normal or gnathopod 1 slightly larger 

 than 2; uropod 3 exceeding uropod 1, outer ramus 2-articulate, inner 

 variable, long or short; telson deeply cleft; no dorsal teeth or carinae, 

 urosome with dorsal spine-bundles. Marine and brackish species: 

 13-15, arctic (boreal in Atlantic), httoral. See "Marine Carinate 

 Gammarus" (p. 244). 



Hornellia Walker 



Hornellia Walker, 1904. 



Type-species: H. incerta Walker, 1904 (monotypy). 



Accessory flagellum 2-articulate; inner lobes of lower lip obsoles- 

 cent; [inner plate of maxilla 1 undescribed], inner plate of maxilla 2 

 densely setose on medial edge; gnathopods normal; uropod 3 not 

 exceeding uropod 1, rami equal, broadly lanceolate, outer 1-articulate; 



