BY MARGUERITE HENRY. 565 



This genus comi^rises a somewhat heterogeneous collection of forms; it cor- 

 responds to Schmeil's "phaleratus-affinis-fimbriatus" gi-oup. Three species occur 

 in New South Wales. 



Key to species of Platycyclops. 

 A. Caudal rami short, not attaining the length of the last two abdominal segments 

 combined. 



B. 5th pair of legs represented on each side by three spines. . . phaleratus. 

 BB. .5th pair, each consisting of a lamella bearing a spine and two setae. 



affinis. 

 AA. Caudal rami long, exceeding the length of the last two segments combined. 



fimbriatiis. 



Platycyclops PHAiERiius (Koch). (Plate Iviii., fig. 1-2.) 



Syn. C. canthocarpoides Fischer, C. lascivius Poggenpol. 



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



Female. Cephalothoras short and broad, the greatest width occurring about 

 the middle and equal to two-thirds of the length; lateral parts of the last segment 

 produced, hairy. Abdomen strongly built, the posterior edges of all the segments 

 denticulated; genital segment short and broad, scarcely as long as the next two 

 segments combined; caudal rami short, bearing rows of spines. Antennules much 

 shorter than the first segment of the cephalothoras, composed of ten segments. 

 Natatory legs with a' broad basal segment; in the 1st, 2nd and 3rd pairs, the 

 terminal segment of the exopodite bears three coarse spines outside, the 4th pair 

 bears only two. Fifth pair replaced on each side by three ciliated spines at- 

 tached to the lateral corners of the corresponding segment. Length, 1.1 mm. 



Distribution. — N.S.W. : Kendall, Berrima, University, Centennial Park, 

 Botany; New Guinea; Ceylon; Turkistan; Europe; North and South America. 



Platycyclops affinis Sars. (Plate Iviii., fig. 3-1.) 



Syn, C. pygmoeus Rehberg. 



Described by Sars in 1863 (p. 47) and first recorded by him from Australia 

 in 1896. 



Female. Cephalothorax narrower than in the preceding species, first seg- 

 ment very long, last segment with the lateral parts slightly produced, bearing 

 spinules. Abdomen with the genital segment slightly dilated at the base; caudal 

 rami longer than in the preceding species. Antennules shorter than the first 

 segment of the cephalothorax and composed of eleven segments. Natatory leg's 

 with the basal part narrower than in P. phaleratus, the terminal segment of the 

 exopodite in the 1st and 2nd pairs with three spines outside, in 3rd and 4th pairs 

 with only two. Fifth pair well defined, consisting of a small lamella bearing a 

 slender spine, and outside a seta of the same length and in tlie middle a smaller 

 seta. Length, . 75 mm. 



Distribution. — This is a comparatively rare species in New South Wales; it 

 has only been found near Sydney and at Mt. Kosciusko. It occurs in China and 

 Turkistan and throughout Europe. 



Platycyclops fimbeiatus (Fischer). (Plate Iviii., figs. 5-6.) 



Syn. C. crassicornis Sars. 



Described by Fischer in 1853 (p. 94), fii'st recorded from Australia by the 

 present author in 1919. 



