116 U.S. NIATIONAL MUSEUM BULLETIN 271 



Outer lobes of lower lip not notched nor medially excavate, outer ramus of 

 uropod 3 not bearing giant hooked spines (except Jassa), occasionally 

 bearing small distal hook, or bent and serrate spine, rami lanceolate or 

 styliform 3 



3. Peduncle of uropod 3 often nearly as long as or longer than peduncle of uropod 



2, rami of uropod 3 much shorter than peduncle, outer ramus of uropod 

 3 distally hooked (hook a giant spine in Jassa), or with minute distolateral 

 denticles, pectinae or serrations (and see Parapherusa in Gammaridae). 



(fig. 49) ISCHYROCERIDAE (p. 275) 



Peduncle of uropod 3 usually much shorter than peduncle of uropod 2, or 

 rami of uropod 3 subequal to or longer than peduncle, or outer ramus of 

 uropod 3 not distally hooked and lacking distolateral ornamentation . 4 



4. Urosome depressed 5 



Urosome not depressed 7 



5. All urosomites coalesced, uropods 1-3 of highly diverse structure (fig. 53). 



CHELURIDAE (p. 180) 



Urosomites rarely all coalesced, uropods 1-2 (but rarely 3) similar to each 

 other and of normal gammaridean form 6 



6. Urosomite 1 elongate (fig. 52) podoceridae (p. 426) 



Urosomite 1 not elongate (fig. 51) corophiidae (p. 184) 



7. Gnathopods 1-2 feeble, subequal to each other, simple or nearly so, article 3 



of mandibular palp vestigial (fig. 165e), article 1 of primary flagellum of 

 antenna 1 elongate, plates of maxilliped foliaceous. 



Synopia (Synopiidae) (p. 462) 

 Gnathopods 1-2 strong, usually dimorphic and subchelate, article 3 of man- 

 dibular palp strong, article 1 of primary flagellum of antenna 1 not elongate, 

 plates of maxilliped not foliaceous 8 



8. Gnathopod 1 larger than 2 (fig. 48) 9 



Gnathopod 2 larger than 1 or gnathopods equal in size 10 



9. Telson thick and fleshy, perepods glandular aoridae (p. 147) 



Telson thin dorsoventrally, pereopods not glandular. 



Falklandella ^ (Gammaridae) (p. 241) 



10. Telson thick and fleshy, pereopods usually glandular. 



(fig. 47) ISAEIDAE (p. 264) 

 Telson thin dorsoventrally, pereopods not glandular 11 



11. Accessory flagellum exceeding three articles. 



(exceptional) gammaridae (p. 231) 

 Accessory flagellum 2-articulate or less, often absent 12 



12. Coxae 1-4 strongly or weakly acuminate midventrally or coxae midventrally 



excavate to form weak or strong anterior and posterior acuminations. 



(exceptional) paramphithoidae (p. 389) 

 Coxae 1-4 rounded or quadrate ventrally. 



(exceptional) calliopiidae (p. 167) 



2 Schellenberg (1931) writes that coxa 4 is distinctly excavate posteriorly but no figure is given and such 

 excavation must be deep and distinct to avoid placing a genus in section H. 



