GAMMARIDEAN AMPHIPODA 



41 



Table 2. — Characteristics of genera in the tryphosa section (see table 1, p. 38, for 



legend). 



•Type-speclcs synonymous with Orchontene. 



tion of mandibular palp article 3 is intragenerically variable. The 

 incision of the inner ramus of uropod 2 is consistently present in the 

 species assigned to Schisturella and absent from those of Hijjpomedon. 

 Telsonic clefts vary to some extent although a slight progression occurs 

 in table 1 from the fully cleft condition of Hippomedon to the poorly 

 cleft condition of Pseudonesimus and the "lakotas." Lobation of the 

 upper lip occurs in the lakotas and Schisturella but not in Pseudo- 

 nesimus^ Paracentromedon^ Elimedon, or Hippomedon. Gnathopodal 

 and epimeral conditions are ignored. 



Despite the intrasectional variability of first coxae, mandibular 

 molars, uropodal incisions, telsons, and upper lips, the outer lobe of 

 maxilla 1 differs fairly consistently between the two sections. The 

 main terminal group of 5 or 6 spines on the outer lobe of maxilla 1 con- 

 sists of very stout members in hippomedons, and thin members in try- 

 phosas. Tlio type-species of Schisturella is slightly aberrant in its 

 maxillary spines. 



Intergradations between the characters of the types of H ippomedon 

 and Schisturella are seen not only in those species now assigned to 

 Paracentromedon but also in several species now assigned to Hippom- 

 edon. Indeed, because it is like ''''Tryphosa^'' the first coxa of Hippom- 



