108 U.S. NATIONAL MUSEUM BULLETIN 271 



elongate but telson always (except Synopia with large accessory flagellum) 

 longer than and generally twice as long as peduncle of uropod 3, cleft or 

 entire synopiidae (p. 454) 



13. Pereopods 3-5 strongly spinose or setose and with elongate setae ("fossorial," 



see glossary) (figs. 97-99) 14 



Pereopods 3-5 poorly spinose or setose or not fossorial 19 



14. Pereopod 5 conspicuously elongate, at least 1.5 times longer than pereopods 



3-4 '. . . OEDICEROTIDAE (p. 373) 



Pereopod 5 not conspicuously elongate, subequal to, shorter than or slightly 

 longer than pereopod 4 15 



15. Telson elongate, nearly twice as long as peduncle of uropod 3 or urosomite 



3 (exceptional) synopiidae (p. 454) 



Telson not elongate, scarcely exceeding length of peduncle on uropod 3 or 

 urosomite 3 16 



16. Base of primary flagellum of antenna 1 conjoint, thus article 1 of flagellum 



longer than peduncle (fig. 34a) . (exceptional) vitjazianidae (p. 476) 



Base of primary flagellum of antenna 1 multiarticulate, article 1 of flagellum 



less than half as long as peduncle 17 



17. Rostrvim usually evanescent, pereopod 5 usually similar to pereopod 4 in 



structure; when pereopod 5 shorter than and of different structure than 

 pereopod 4 then rostrum absent (fig. 45). 



(See Sancho in Calliopiidae) 18 

 Head with distinct, and depressed or downturned, rostrum, pereopod 5 

 always shorter and of different structure than pereopod 4 (fig. 44). 



PHOXOCEPHALIDAE (p. 412) 



18. Check the individual through the family key of Haustoriidae. Most haus- 



toriids will be detected in the first 15 couplets. If one of the following 

 characters does not apply to the species, proceed to Gammaridae: (1) 

 pereopod 5 much shorter than 4 and article 2 lamellar (Pontoporeia and 

 Urothoides) ; (2) mandible immense, triturating surface large and smooth, 

 distal, palp relatively small and thin, and nearly asetose (Carangolia) ; (3) 

 article 2 of maxilla 1 palp shorter than article 1 (Phoxocephalopsis) ; (4) 

 mandibular incisor unproduced and teeth absent or obsolescent and article 

 6 of pereopods 1-2 with stout spines {Urothoe and Urothoides). 



HAUSTORIIDAE (p. 248) and gammaridae (p. 231) 



19. Some anterior coxae acuminate midventrally (fig. 36), and accessory flagel- 



lum less than 3-articulate. 



PARAMPHITHOIDAE (p. 389) and ACANTHONOTOZOMATIDAE (p. 117) ^ 



Anterior coxae not acuminate midventrally, or if acuminate then accessory 

 flagellum more than 2-articulate 20 



20. Article 4 of pereopods 1-2 extremely elongate relative to other articles, palp 



of one member of first maxillae distinctly geniculate and scaled. 



(fig. 33) HYPERIOPSIDAE (p. 261) 



Article 4 of pereopods 1-2 not elongate, palp of maxilla 1 neither strongly 

 geniculate nor scaled 21 



21. Telson entire (often with minute notch or shallow emargination) ... 22 

 Telson cleft 26 



3 See also Halirages stebbingi Schellenberg (1931) (=H. huxleyanus Stebbing, 1888, not Bate) in family 

 CaUiopiidae. Note that almost all acanthonotozomatids have a nontriturative mandibular molar or no 

 molar whereas almost all Paramphithoidae have triturative molars. Acanthonotozomatidae usually have 

 conically grouped mouth parts from lateral view whereas most Paramphithoidae have mouth parts grouped 

 in a quadrate bundle. See text for further discussion. 



