430 SPHiEROMIDJE. 



ISO POD A. SPH^ROMIDjE. 



NORMA LIA. 



Genus — N^SA. {Leach). 



(Nes^a — White. N^esea — M. Edwards.) 



Generic character. With the sixth segment of the pereiou 

 enlarged, cand dorsally produced into a strong bidentate process. 

 Pleon with the upper surface irregular and setose. Uropoda 

 with the articulated ramus greatly elongated. 



The dorsal surface of the body is smooth, but the 

 sixth segment is slightly rugose, and is armed at its hind 

 margin with two sharp processes extending over the tail, 

 which has the upper surface irregular, with two large 

 rounded tubercles in the middle : the outer plate of 

 the lateral appendages of the tail is greatly elongated, 

 and extends considerably backwards, whilst the inner plate 

 is fixed, and transversely directed inwards, nearly meeting 

 the corresponding division of the opposite appendage 

 behind the middle of the hind margin of the tail. This 

 peculiar structure of the tail and its appendages prevents 

 the animal from rolling itself into a ball in the same 

 manner as the Spharomae, with which, in other respects, 

 these animals are nearly allied. The nearest approach is, 

 however, inade to Dijnamene Montagui, in which the 

 sixth segment of the body shows traces of the two pro- 

 cesses of N(ssa in the bipartite tubercle of its posterior 

 margin. 



The upper antennse are separated at the base by an 

 oblong protuberance ; the basal joint is thick, oblong, 

 and rugose; the second joint small, with the apical angles 

 acute; the flagellum multiarticulate. 



