366 EEV. A. M. NORMAN AND ME. G. S. BEADY 



1853. Lathonura rectirostris, Lilljeborg. De Crust, ex Ord. 

 tribus, Clad. Ostrac. et Copep., p. 57. PL IV, figs. 

 8-11 ; PL VI, fig. 2; and PL XXIII, figs. 12, 13. 



1860. Pasithea lacustris and rectirostris, Leydig. Naturges. 

 der Daphniden, p 203. PL VII, fig. 57 ; and p. 200. 



Carapace obovate, dorsal margin sinuated at the junction of 

 the head and thorax, posteally well arched, valves of carapace 

 united as far as the middle of the posterior extremity, beyond 

 which they are extended downwards in a semicircular form, so 

 that the ventral side of the carapace is the longer, and the infero- 

 posteal angle is completely rounded off; ventral margin nearly 

 straight in its central portion, having the anterior two-thirds of 

 its length fimbriated with a series of curious flattened, lanceolate 

 plates, of considerable size ; posterior third furnished with fine 

 short cilia, the line of separation between the fimbriating plates 

 and the cilia is sharply defined. Head very large, rostrum 

 scarcely any ; eye small, near the summit of the head ; eye-spot 

 very minute, situated at a considerable distance from the eye, 

 and close to the origin of the anterior antennae ; anterior antenna? 

 long, narrow, cylindrical, of nearly equal width throughout, edges 

 slightly notched, one conspicuous spine-like seta on the anterior 

 and a second on the posterior margin ; distal extremity truncate, 

 furnished with tentaculiform setae ; posterior antennas having the 

 peduncle long and slender, crenated at the base ; each ramus fur- 

 nished with five setae, and a terminal spine ; the setae all alike, 

 short, geniculate, and plumose, and differing from the usual an- 

 tennal setse of the family in that the basal portion is much thicker 

 than the terminal portion; the lowermost seta of the three-jointed 

 ramus in no way differs from the rest ; but two of the terminal 

 setae of each ramus have their basal portion (instead of being plu- 

 mose) furnished on one edge with small spines. Abdomen of very 

 peculiar form, very small, and consisting chiefly of a mammaeform 

 process produced backwards and downwards, to the extremity 

 of which are attached the abdominal setae, which are of great 

 size and length, sparingly plumose, not geniculate, but having 

 their extremity multiarticulate ; terminal claws very small ; the 



