364 REV. A. M. NORMAN AND HR. G. S. BRADY 



in the non-genioulated structure of the first seta of the three- 

 jointed ramus of the posterior antenna?. 



Drepanothrix hamata, G. 0. Sars. PI. XXII, figs. 5-7. 



1861. Drepanothrix sentigera, G. 0. Sars. Om dei omegnen af 



Christiania forekommende Cladocerer, p. 14. 



1862. Drepanothrix hamata, Gr. 0. Sars. Om de i omegnen af 



Christ, forekom. Clad. Andet JBidrag., p. 51. 



Carapace showing a distinct separation of the head from the 

 thorax, marked by a sinuation at their junction on the dorsal mar- 

 gin ; form of the hinder portion (as apart from the head) nearly 

 round ; a remarkable large thorn-like process (which is however 

 very variable in size and sometimes almost obsolete) projecting 

 from the middle of the dorsal margin, both margins well arched ; 

 valves united as far as the middle of the posterior extremity; ven- 

 tral margin serrulated, and fringed with long, simple seta? ; surface 

 both of head and valves regularly and distinctly punctated and 

 reticulated, reticulations sexangular. Head large, erect, rostrum 

 pronounced ; eye large, eye-spot half the size of the eye, quad- 

 rangular ; anterior antenna? dependent from the extremity of the 

 rostrum, large, gently curved, distal half of the anterior margin 

 having a series of deep notches, about six in number, extremity 

 truncate and furnished with tentaculiform cilia; posterior antenna? 

 having the peduncle of moderate size, crenated at the base, and 

 with a long acute spine on the upper side at its extremity ; four- 

 branched ramus furnished with a spine at the extremity of the 

 second articulation, and terminating in three geniculate plumose 

 seta? and a spine ; three-jointed ramus, having the seta of the 

 basal joint flattened, curved, not jointed, and margined towards 

 the end on one side with spines, second joint furnished with one 

 (longer than the others) and ultimate joint with three geniculate 

 plumose seta? and a spine. The labrum is produced downwards 

 in the form of a large, thickened angular process. Abdomen small 

 but very deep, not more than twice as long as broad, edged with 

 spines, and having oblique rows of very delicate setiform spines 

 on the sides ; extremity wide, emarginate ; claws small, curved, 



