130 MR. a. S. BKADY ON THE CRUSTACEAN FAUNA OF THE 



Family. HARPACTIDiE. 



Genus. TACHIDITJS, Lilljehorg. 



Superior antennae short, having no flagellum ; in the male 

 bearing a vesicuHform appendage, and hooked at the extremity, 

 in the female stout, and densely setose. Lower antennae small, 

 two-branched ; secondary branch small. First four pairs of 

 swimming feet alike, two-branched ; each branch tri- articulate ; 

 fifth pair rudimentary, and composed of a single setose lamina. 

 One eye. Ovisac single. 



Tachidius bkevicornis (Muller). (Plate V., figs. 1-9.) 



Cyclops brevicornis, Muller. Entomostraca, p. 118. 



Tachidius brevicornis, Lilljeborg. De Crust, ex Ord. trib., p. 

 196, Tab. XXII., figs. 12-16; Tab. XXIII., figs. 1, 2, 9; 

 and Tab. XXIV., figs. 17, 18. 



Body gradually tapering from the head downwards ; lower 

 edge of each segment distinctly pectinated ; head beaked. First 

 segment of the cephalothorax equal in length to the following 

 three. Superior antennae of the female (fig. 4) swollen at the 

 base, the last five joints suddenly narrower, last joint excessively 

 small, penultimate longer than any of the three preceding ; the 

 whole antenna densely clothed with long setae on its upper mar- 

 gin, some of the setae being strongly plumose, or even almost 

 spinous. Superior antenna of the male (fig. 3) bearing, towards 

 the apex, a large vesiculiform sac from the upper margin of which 

 spring a strong curved spine and three long setfe ; the apex of 

 the antenna forming a strong claw or hook. Lower antennre 

 (fig. 5) two-jointed, the basal joint bearing a small, slender, 

 secondary branch. Third foot-jaw (fig. 6) tri-articulate, slender, 

 chelate. Four pairs of swimming feet (fig. 7), all alike, two- 

 branched, each branch three-jointed. Fifth pair (fig. 9) squa- 

 mous, bordered with long spiniform set®. Terminal joints of 

 the abdomen very short (fig. 8) ; internal (longer) setae of the 

 tail about half the length of the body, external set* half the 



