67 



39. Pachycyclops bistriatus (Koch). 



(PI. XLI). 

 Cyclops bistriatus, Koch, 1. c. Heft 21, Tab. 7. 



Syn : Cyclops distinctus, Richard. 

 gracilicornis, Lande. 



Specific Characters. Female. Anterior division of body regularly oval 

 in outline, greatest width somewhat exceeding half the length and occurring about 

 in the middle. Tail comparatively short, scarcely attaining half the length of the 

 anterior division ; genital segment somewhat shorter and broader than in P. sig- 

 natus. Caudal rami a little more produced, though scarcely attaining the length 

 of the last 2 segments combined; apical setae rather spreading and exhibiting 

 nearly the same mutual relation in length as in the preceding species. Anterior 

 antennas still more slender and elongated than in that species, reaching, when 

 reflexed, even to the end of the 4th segment, lateral rib of the outer joints incon- 

 spicuous. Posterior antennse of normal structure, the penultimate joint being much 

 shorter than the terminal one and also distinctly thicker ; apical setae, as usual, 

 gradually increasing in length inwards. Both pairs of maxillipeds conspicuously 

 smaller than in the preceding species. Natatory legs with the rami compara- 

 tively broader; terminal joint of inner ramus in 4th pair somewhat curved in the 

 middle, and having the apical spines less unequal, the inner one conspicuously 

 bent inwards. Last pair of legs resembling in structure those in the preceding 

 species, though having the distal joint comparatively larger in proportion to the 

 proximal one. Ovisacs rather large and slightly divergent. Seminal receptacle 

 with the posterior psrrt rather produced and very conspicuously bipartite. 



Body of a dark blue colour, with the anterior part of the cephalic seg- 

 ment somewhat lighter. 



Length of adult female about 2.20 mm. 



Remarks. I think I am right in identifying the above-described form 

 with Cyclops bistriatus of Koch. The figure given by Koch applies fairly well 

 to the present form, and also his notes about the colour agree. In any case it 

 is evident that the figure represents a true Pachycyclops, and as the 2 other 

 species are both very recognisably figured by that author, the said figure cannot 

 refer to any other species than the one here under discussion. As Koch's name 

 has the precedence both to that given to the species by Dr. Richard, and to that 

 proposed by A. Lande, it ought to be retained for the present species, though it 

 is somewhat inappropriate, being apparently derived from the anteriorly some- 

 what divergent dark ovarial tubes shining through the body. Dr. Schmeil at 

 first opined that this form was merely a hybrid between th.e 2 other species; but 



