90 



U.S. NATIONAL MUSETTM BULLETIN 271 





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Figure 39. — -Eusiridae: a, lower lip, with or without inner lobes [see shape of lower lip of 

 Pleustidae, Astyridae]; h, accessory flagellum, absent, uni- or biarticulate [see Gammaridae 

 which have a few species with 2-articulate accessory flagella]; c,d, uropods 1, 2, note 

 shortened outer rami [most Gammaridae do not]; e,j, extremes of telson [see Calliopiidae, 

 Pleustidae]. 

 Astyridae have nontriturative mandibular molars but all Eusiridae except Eusirella have 

 strongly triturative molars. Vitjazianidae have simple first gnathopods and basally con- 

 joint primary flagella of antenna 1. Synopiidae have massive heads with deflexed rostra, 

 usually have multiarticulate accessory flagella and feeble gnathopods whereas most Eusiridae 

 have powerful gnathopods. Oedicerotidae have pereopod 5 disproportionately elongate 

 in comparison with pereopods 3 and 4. Paramphithoidae always have the unique combina- 

 tion of feeble gnathopods and one or more acuminate coxae 1—4. Liljeborgiidae have the 

 unique combination of powerful gnathopods and nontriturative mandibular molar. Gam- 

 maridae have pleonites 1-3 together not exceeding length of 5 pereonites together, whereas 

 Eusiridae have these pleonites (metasome) exceeding six pereonites in length; all Eusiridae 

 except one genus have elongate telsons, whereas Gammaridae have short telsons not or 

 scarcely exceeding the length of pleonite 6. 



