MARINE GAMMARIDEAN AMPHIPODA 33 



the two genera. Again, some resemblance to the eusirid grade of struc- 

 ture is seen in the elongate enfeebled gnathopods characteristic of some 

 calliopiids, but gnathopod 1 is almost completely simple, the accessory 

 flagellum is 3-articulate and elongate as in some vitjazianids, and, 

 furthermore, the palp on one member of the first maxillae is specially 

 modified, bent and scaly. Article 4 of pereopods 1-2 is enormously 

 elongate, thus giving to the pereopods a strong raptorial function 

 apparently surrendered by the gnathopods. 



Argissidae fall as a sidebranch of the gammarid families into the 

 eusirid grade of structure by reduction of the accessory flagellum to 

 2-articles. Such reduction by itself does not imply any direct rela- 

 tionship to those eusirid families for some marine and nonmarine 

 Gammaridae also have a reduced accessory flagellum ; such reduction 

 occurs repeatedly in other completely distinct groups (e.g., isaeids). 

 The peculiar coxal morphology of argissids (fig. 43) is not fully unique, 

 for an analogous condition occurs in a gammarid genus, Megaluropus. 

 Enfeeblement of gnathopods is again a feature of argissids but the 

 quadrilocular eyes of oculate members seem significant. Except for 

 those eyes, the diagnostic characters of argissids, though unique to- 

 gether, are drawn from diverse members of the Gammaridae. 



Pardaliscidae are a very difficult puzzle. They are perhaps the most 

 aberrant of the gammarid families, although synopiids rival them. 

 Once the principle has been established that the presence of a well- 

 developed accessory flagellum probably marks a gammarid family, 

 or a noneusiridean branch, the Pardaliscidae are to be kept within the 

 gammarid block. But they are characterized by foliation of the man- 

 dibles and loss of molars, the frequently occurring conjoint condition 

 at the base of the primary flagellum on antenna 1, feeble gnathopods, 

 progressively reduced coxae, and one or more peculiarities of the maxil- 

 lipeds : reduction in overall size of the inner plates, often a reduction 

 in the outer plates, and, occasionally, an elongation of the article 

 carrying the outer plates. The lower lip often has the inner lobes 

 coalesced and forming a convex bridge between the outer lobes. A 

 generalized view of the maxillipeds suggests affinities with the Lil- 

 jeborgiidae in which the maxillipedal palps, like those of the Par- 

 daliscidae, are relatively dominant over the basal plates. The mandibles 

 of Liljeborgiidae show a strong tendency to a complete loss of the 

 molars but liljeborgiid gnathopods are veiy powerful and the lilje- 

 borgiid with the smallest coxae has larger coxae than any pardaliscid. 

 The lower lip of liljeborgiids could be precursive to that of pardaliscids. 



The powerful gnathopods of the Liljeborgiidae are reminiscent of 

 those in the Eusiridae (Rhachotropis) but most liljeborgiids have a 

 strongly developed accessory flagellum and all have a reduced, non- 

 triturative molar. Some eusirids also have this reduced molar. The 



