112 U.S. NATIONAL MUSEUM BULLETIN 271 



Mandibles, lower lip and maxillae present. 



(exceptional) leucothoidae (p. 289) 



6. Uropod 3 biramous 7 



Uropod 3 uniramous 10 



7. Coxa 4 not excavate posteriorly, pereopods 1-2 glandular 8 



Coxa 4 excavate posteriorly, pereopods 1-2 not glandular 9 



8. Rami of uropod 3 shorter than peduncle, outer ramus with distal hook or 



distolateral denticles, lacking setae. 



(exceptional) ischyroceridae (p. 275) 

 Rami of uropod 3 longer than peduncle, outer ramus setose or spinose but 

 lacking special hooks or denticles. 



(exceptional) isaeidae (=Photidae) (p. 264) 



9. Article 4 of pereopods 1-2 exceptionally elongate (fig. 33/), base of primary 



flagellum on antenna 1 conjoint and forming an article longer than pe- 

 duncle, palp of maxilla 1 geniculate and scaled (figs. 102a, b). 



Parargissa (Hyperiopsidae) (p. 264) 

 Article 4 of pereopods 1-2 not elongate, base of primary flagellum on antenna 

 1 not conjoint, palp of maxilla 1 not geniculate or scaled. 



amphilochidae (p. 132) 



10. Gnathopods simple and slender, with dense setae as long as fifth and sixth 



articles, all coxae at least as broad as long. 



(exceptional) isaeidae (=Photidae) (p. 264) 



Gnathopods usually subchelate and one pair usually stout, if not then their 



setae very short and sparse, some coxae very much longer than broad . 1 1 



11. Article 2 of pereopod 3 slender and linear (like fig. 162 z;) 12 



Article 2 of pereopod 3 expanded like pereopods 4-5 (like fig. 162s). 



CRESSIDAE (p. 198) 



12. Urosomal segments coalesced fully or partially, telson thickened dorso- 



ventrally (fig. 17), or gnathopod 2 carpochelate. 



(exceptional) thaumatelsonidae (p. 473) 



Urosomal segments separate, telson depressed (fig. 18), gnathopod 2 never 



carpochelate stenothoidae (p. 444) 



SECTION E 



Uropod 3 essentially uniramous, lacking rami or occasionally absent; when 

 present inner ramus scalelike and outer ramus cylindrical; Cheluridae partially 

 included herein although outer ramus flat ; observer urged to verify that one ramus 

 of uropod 3 not accidentally broken off. 



1. Mandibular molar bearing grinding ridges (triturative) or if not triturative 



then molar cupshaped 2 



Mandibular molar smooth or bearing a few articulate spines, or molar 

 absent or not cupshaped 10 



2. Mandibular palp present 3 



Mandibular palp absent 6 



3. Urosomite 1 elongate, longer than metasomite 3 and more than twice as 



long as urosomite 2 (fig. 52) podoceridae (p. 426) 



Urosomite 1 not elongate as above 4 



4 . All urosomites coalesced 5 



Urosomites separate 8 



5. Uropods 1-2 of strongly diverse structure (fig. 53) . cheluridae (p. 180) 

 Uropods 1-2 normally styliform, although occasionally with rami or ped- 

 uncles reduced in size (fig. 51) corophiidae (p. 184) 



