MARESTB GAMMARIDEAN AMPHIPODA 109 



22. Accessory flagellum 2-articulate 23 



Accessory flagellum 1-articulate or absent 24 



23. Rami of uropod 3 cylindroconical, much shorter than elongate peduncle. 



Bathyphotis (Ischyroceridae) (p. 275) 

 Rami of uropod 3 lanceolate or flabellate, much longer than peduncle. 



(exceptional) gammaridae (p. 231) 



24. Lower lip with unpointed, tilted, oval lobes astride partially coalesced inner 



lobes (fig. 37) PLEusTiDAE (p. 421) 



Lower lip with tilted or untilted outer lobes but with distinct mandibular 

 extensions, inner lobes when present not coalesced (fig. 38), (examine also 

 key to Eusiridae if telsonic condition dubious) 25 



25. Telson longer than wide calliopiidae (p. 167) 



Telson as wide as or wider than long .... (exceptional) gammaridae 



26. Article 1 of primary flagellum on antenna 1 as long as peduncle. 



viTJAziANiDAE (p. 476) and (exceptional) male synopiidae (p. 454) 

 Article 1 of primary flagellum on antenna 1 not longer than half of pe- 

 duncle 27 



27. Telson elongate (fig. 39), twice as long as peduncle of uropod 3 .... 28 

 Telson rarely longer than peduncle of uropod 3, never twice as long as 



peduncle of uropod 3 30 



28. Urosomite 3 twice as long as urosomite 2, head with anterodorsal margin 



extended as blunt plow (fig. 66d) . Pseudotiron (Synopiidae) (p. 461) 



Urosomite 3 less than 1.5 times as long as urosomite 2, head of normal 



dimensions as in basic gammaridean 29 



29. Accessory flagellum 3+-articulate . . (exceptional) synopiidae (p. 454) 

 Accessory flagellum 0-2-articulate (examine also key to Calliopiidae if 



telsonic cleft dubious) eusiridae (p. 213) 



30. Inner ramus of uropod 3 short and scale-like (fig. 96c). 



(exceptional) gammaridae (p. 231) 

 Inner ramus of uropod 3 elongate 31 



31. Rami of uropod 3 foliaceous .... (exceptional) gammaridae (p. 231) 

 Rami of uropod 3 lanceolate 32 



32. Mandibular palp article 2 shorter than article 1. 



(exceptional) gammaridae (p. 231) 

 Mandibular palp article 2 longer than article 1 33 



33. Gnathopod 1 simple (exceptional) gammaridae (p. 231) 



Gnathopod 1 subchelate 34 



34. Accessory flagellum 2+-articulate gammaridae (p. 231) 



Accessory flagellum 1-articulate or absent eusiridae (p. 213) 



SECTION B 



1. Head and body strongly depressed, rugose, coxae splayed (fig. 10). 



PHLIANTIDAE (p. 405) 



Head subglobular, body cylindrical (fig. 8?;), coxae short, not splayed. 



(exceptional) eophliantidae (p. 209) 



Head compressed or subglobular, body compressed laterally, rarely rugose, 



coxae never splayed 2 



2. Article 2 of antenna 1 shorter than or equal to article 1, uropod 3 usually 



biramous but when uniramous then article 2 of antenna 1 not elongate or 



gnathopod 1 not chelate 3 



Article 2 of antenna 1 much longer than or equal to article 1 (fig. 15), uropod 3 

 always uniramous, gnathopods strongly chelate . . . sebidae (p. 435) 



