MARINE GAMMARIDEAN AMPHIPODA 315 



17. Gnathopod 1 simple ^ 18 



Gnathopod 1 distinctly subchelate ^ 31 



18. Coxa 1 reduced or distinctly tapering from base and often strongly hidden 



by coxa 2 19 



Coxa 1 large, rectangular and not hidden, taper if present occurring in 

 only distal third of coxa 26 



19. Pereopods prehensile Metacyclocaris 



Pereopods simple 20 



20. Maxillipedal palp with three articles, telson entire Perrierelia 



Maxillipedal palp with four articles, telson cleft 21 



21. Maxillipedal palp article 4 vestigial (fig. 128a) 22 



Maxillipedal palp article 4 well developed and claw-like 23 



22. Mandibular molar present, upper lip and epistome coalesced, epistomal 



region strongly produced Centromedon 



Mandibular molar absent, upper lip and epistome separated by notch, 

 upper lip slightly protruding Ambasia 



23. Inner plate of maxilla 2 much broader than outer plate and usually gaping 



mediad Aristias 



Plates of maxilla 2 subequal in width and not strongly gaping 24 



24. Upper lip and epistome not differentially produced, small and inconspicuous. 



Uristes 

 Upper lip projecting as lobe in front of epistome (from lateral view) . . 25 



25. Outer plates of maxiUiped lacking spines, gnathopod 1 weakly subchelate, 



coxa 1 nearly as long as article 2 of gnathopod 1 Ambasiopsis 



Outer plates of maxiUiped spinose, gnathopod 1 perfectly simple, coxa 1 

 about half as long as article 2 of gnathopod 1 Metambasia 



26. Inner plate of maxilla 1 fully lined medially with eight or more setae. 



AUcella 

 Inner plate of maxilla 1 with three or fewer terminal setae 27 



27. Inner ramus of uropod 3 vestigial, less than one third length of outer. 



Clepidecrella 

 Inner ramus of uropod 3 subequal to outer 28 



28. Telson cleft one third or more 29 



Telson entire or emarginate 30 



29. Gnathopod 1 perfectly simple, slender, substyliform, dactyl strong and 



bearing posterior setal brush near base (fig. 130z) Ichnopus 



Gnathopod 1 perfectly simple, slender, dactyl strong and lacking posterior 



setal brush Menigratopsis 



Gnathopod 1 weakly subchelate, of medium stoutness, dactyl strong but 



lacking posterior setal brush although bearing small accessory tooth. 



Paronesimus 



30. Labral region of prebuccal complex with strongly acute anterior lobe [telson 



longer than broad] Paralysianopsis 



Labral region of prebuccal complex with anteriorly rounded keel or unpro- 

 duced [telson as broad as long in Paralibrotus only]. 



Menigrates (in part), Paralibrotus 



31. Coxa 1 reduced or distally tapering from base and often strongly hidden by 



coxa 2 32 



Coxa 1 large, rectangular and not hidden by coxa 2, taper if present occurring 

 only in distal third of coxa 42 



32. Inner plate of maxilla 1 with three or more setae 33 



Inner plate of maxilla 1 with two or fewer setae (or inner plate absent) . 35 



2 Some latitude is expressed in this division as certain genera are found in both pathways. 



285-135 O - 69 - 21 



