MARINE GAMMARIDEAN AMPHIPODA 311 



25. Setae of inner plate on maxilla 1 mostly terminal, mandibular molar ex- 



tremely broad even though laminate and subconical, with girdle of ridges 

 or setules (pleonite 3 with dorsal notch), mandible when flattened, 

 with deep S-shaped insinuation between palp and incisor (fig. 126d). 



Eurythenes 

 Setae of inner plate on maxilla 1 medial only or medial and terminal, man- 

 dibular molar "absent" or long, narrow, conical and lacking distinct 

 girdle (apparently pleonite 3 dorsally smooth), mandible when flattened 

 with shallow concavity between palp and incisor 26 



26. Coxa 1 longer than broad, ovatorectangular, as long as its article 2, lobes of 



maxilla 2 equally broad Paralicella 



Coxa 1 as broad as long and subquadrate, and only two thirds as long as its 

 article 2, inner lobe of maxilla 2 much broader than outer (lobes often 

 gaping) Aristias 



27. Mandibular molar lacking setules Lepidepecreopsis 



Mandibular molar strongly setulose 28 



28. Head small, cpistome and upper lip small and inconspicuous . . . Uristes 

 Head of normal size, epistome and upper lip large and conspicuous, epistome 



usually slightly lobate 29 



29. Article 7 of gnathopod 1 with accessory tooth. 



some species of "Tmetonyx ' auct. [^Tryphosella] 

 Article 7 of gnathopod 1 simple .... Tryphosella [="Tryphosa" auct.] 



KEY O 



1. Pereopods 1-5 prehensile (fig. 130d). . Metacyclocaris 



Pereopods 1-5 not prehensile 2 



2. Lobes of maxilla 2 gaping, and/or inner lobe much broader than outer 



(fig. 127 j), mandible with molar and gnathopod 1 nearly simple . Aristias 



Lobes of maxilla 2 appressed and of intersimilar shape, characters not in 



similar combination 3 



3. Gnathopod 1 simple 4 



Gnathopod 1 subchelate, even though weakly 7 



4. Mandible lacking molar (or if rudiment present, palp attached proximal to 



molar) 5 



Mandible bearing molar 6 



5. Article 2 of maxillipedal palp less than half as broad as outer plate. 



Centromedon and Ambasia 

 Article 2 of maxillipedal palp much broader than outer plate . Ambasiella 



6. Outer plates of maxillipcd with spines Metambasia • 



Outer plates of maxilliped lacking spines Ambasiopsis 



7. Inner plate of maxilla 1 with one or two immense falcate setae (fig. I27d). 



Hirondellea - 

 Inner plate of maxilla 1 with small, slender setae 8 



8. Inner ramus of uropod 2 dorsally notched or constricted 9 



Inner ramus of uropod 2 simple 11 



9. Gnathopod 1 subchelate 10 



Gnathopod 1 weakly chelate (fig. 129a) Aristiopsis 



10. Coxa 1 tryphosid in outline (fig. r29A0. 



"Orchomenella" groenlandica (Hansen) 



• Sec Schisturella diagnosis (p. 361). 



• See note, Key N, couplet 23. 



