34 U.S. NATIONAX. MUSEUM BULLETIN 271 



Eusiridae seem to be so broadly polyphyletic that there is cause to 

 investigate the interrelationships of liljeborgiids with some of the 

 eusirids. Several grades of structure are congruent between the 

 Liljeborgiidae and certain members of the Pleustidae. The labia of 

 the two groups are very similar and the mandibular molars of pleustids 

 often resemble those of liljeborgiids. Pleustid gnathopods are often 

 enlarged but the family differs from liljeborgiids in their uncleft telson 

 and vestigial accessory flagellum. The outer rami of uropods 1-3 are 

 shortened in Pleustidae and the outer ramus of uropod 3 is uniarticu- 

 late but some liljeborgiids approach these conditions. The pleustid 

 rostrum is a development restricted to a few members only. 



Synopiidae are retained in close proximity to the basic gammaridean 

 in view of their elongate accessory flagellum, even though several of 

 their members have the articles reduced to two. Gnathopods are 

 feeble. All but a few synopiids have the head enlarged in relation to 

 the shortened pereonites 1-3. Coxa 3 dominates coxa 4 in most of the 

 genera, and in all but one genus, article 3 of the mandibular palp has 

 become very short, almost vestigial. The mouthparts are otherwise 

 basic except for those genera having the molars extremely enlarged 

 and velvety smooth. This semifossorial condition has also occurred in 

 some haustoriids even closer to the Gammaridae than the Synopiidae. 

 Uropods have undergone the eusirid shortening of the outer rami but 

 uropods 1-2 are far more specialized in the frequent sublamellar con- 

 dition of the inner rami. In all but Synopia, the telson has become 

 elongate. Eyes when present are dorsally coalesced or contiguous, 



Oedicerotidae are another group, like the Synopiidae and Parda- 

 liscidae of generally obscure relationships. They have reached the 

 eusirid grade of structure in accessory flagellum, resemble the Syn- 

 opiidae in head and eyes but the telson is a short, thin, ovate or 

 truncato-ovate, uncleft lamina, unlike that of most Synopiidae. 

 Uropod 3 has become fully elongate, a tendency seen in several 

 synopiids but the pereopods have become strongly fossorial, the first 

 four pairs by virtue of their long setae and the fifth pair by virtue of 

 its immense articular elongation. On the average, gnathopods are of 

 medium size, thus being more powerful than those of synopiids. 

 Oedicerotidae have a strong resemblance to isaeids especially in 

 pleonal epimera and pigmentation but lack pereopodal glands and have 

 a thin, nonfleshy telson. 



Three families, each of them highly distinct from one another, seem 

 to have strong relationships to the Eusiridae-Calliopiidae-Pleustidae 

 complex. The least distinct is the Paramphithoidae, a group character- 

 ized by acuminate coxae; several intergrading genera suggest that 

 Paramphithoidae might be incorporated within the broader eusirid 

 amalgam. The Laphystiopsidae carry calliopiid tendencies to a loss of 



