BY MARGUERITE HENRY. 563 



with two unequal spines and a long seta. Seminal receptacle more or lesj bi- 

 partite. 



This genus corresponds to Schmeil's "fusciis-cdbi<hi.s" group. One species is 

 present in N.S.W. 



Pachycyclops annulicornis (Koch). 



Syn. — C. quadrioornis albidus Jurine, C. tenuicornis Glaus, 6'. alhidus Sehmeil, 

 C. gyrinus Forbes. 



Described by Koch in 1835, first recorded from Australia by Sars (1896) 

 and figured in 1908 (Plate iii., figs. 1-4). 



Female. Cephalothorax broadly ov.al in outline, the greatest width exceed- 

 ing half the length. Abdomen long, genital segment cylindrical, equal to the 

 combined length of the three succeeding segments; caudal rami short. Antennules 

 long and slender, reaching beyond the third segment of the cephalothorax, com- 

 posed of seventeen segments, of which the 2nd and 3rd, 10th and 11th are 

 usually darker in colour than the other segments. Antennae with a very long 

 and slender terminal segment. Natatory legs with the terminal segment of the 

 endopodite of the fourth pair distinguished by the rudimentary distal seta. Fifth 

 pair with the distal segment much smaller than the proximal. Length, 1.8 mm. 



Distribution. — This species has a world-wide distribution and is very com- 

 mon in this State. A solitary specimen was raised from dried mud collected at 

 Corona. N.S.W. : Kendall, Bangalow, Pt. Stephens, Parramatta, Five Dock, 

 Centennial Park, National Park, Waterfall, Berrima, Yass, Bringagee; Victoria; 

 South Australia; Hawaii; Asia; Africa; Europe; North and South America. 



Genus Mesocyclops Sars, 1914. 



Cephalothoracic segments scarcely prominent laterally; last segment very 

 small and not produced laterally. Abdomen slender, genital segment elongated, 

 slightly dilated anteriorly; caudal rami of moderate length or very short. An- 

 tennules long and slender, usually composed of seventeen segments. Antennae 

 with the apical setae long and curved. Natatory legs with both rami three- 

 segmented, terminal segment of the exopodite with only two spines outside, ter- 

 minal segment of the endojDodite unusually long. Fifth pair very small, two- 

 segmented, the distal segment carrying two slender setae. Seminal receptacle 

 bilobed anteriorly, the posterior portion somewhat tongue-shaped. 



This genus corresponds to Schmeil's "leuckarti" group. One species occurs 

 in New South Wales. 



Mesocyclops obsoletus (Koch). 



Syn. — C. leuckarti Clans, C. simplex Poggenpol, C. scourfieldi Brady. 



First described by Koch in 1835 and recorded from Australia by Sars in 

 1896. In 1908 Sars described a special variety australiensis for the Australian 

 form. 



Female. Cephalothorax slender, more so than in the typical European form, 

 first segment unusually large and the last very small. Abdomen long and slender, 

 genital segment produced and equal to the leng-th of the three succeeding seg- 

 ments combined; caudal rami less divergent and longer than in the typical form, 

 sometimes slightly exceeding the length of the last two segments combined. An- 

 tennules composed of seventeen segments, long and slender, attaining the end 

 of the third segment. Natatory legs with the spines of the exopodites very 

 coarse. Fifth pair with a narrow distal segment, sqtae long and slender. Length, 

 1.3 mm. 



