FRESH- WATER CYCLOPID^E AND CALANIDJS; 5 



The reference numbers given in the lists of synonyms indi- 

 cate the memoirs to which similar numbers are attached in the 

 appended ''Bibliographical Index." 



Family CYCLOPIA. 

 Geots CYCLOPS, Miiller. 



a. Anterior antennae eighteen-jointed. 



1. Cyclops elongatus, Claus, (PI. I., figs. 1-5). 



1863. Cyclops elongatus, Claus (18), p. 97, pi. XI., figs. 1, 2. 



1871. „ ,, Heller (23), p. 4. 



1880. ,, ,, Kehberg (33), p. 538. 



1883. ,, ,, Cragin(40),p.2, pi. I., figs.l, 19-23. 



1885. „ ,, Daday. (44), p. 207. 



Body gradually tapering from before backwards ; none of the 

 segments much produced laterally, posterior angles of the first 

 three rounded off or obtuse, those of the much smaller fourth 

 and fifth segments somewhat produced backwards and acutely 

 angulated ; abdomen about half as long as the cephalothorax, 

 margins not denticulated ; caudal rami rather stout, about as long 

 as the last two abdominal segments ; principal caudal setae half 

 as long as the body of the animal. Anterior antennae eighteen- 

 jointed, scarcely as long as the first body-segment. The last 

 joint of the outer branch in the second, third, and fourth pairs 

 cf feet has three spines on the outer and three setae on the inner 

 margin, the first of the three spines being smaller than the other 

 two. The fifth foot is two- jointed, the basal joint rather short 

 and wide and bearing a single long seta, the second joint elon- 

 gated, narrow, and having at the extremity a short, awl-shaped 

 spine and a long seta. Length 1*4 mm. 



This species seems to be very uncommon, and has been noticed 

 only by Professor Claus and Eehberg in Germany, by Heller 

 in the Tyrol, and by Cragin in America, where it occurred 

 "sparingly in a rain-pool near the Cambridge Museum of Com- 

 parative Zoology." The chief characteristic of the species is 

 the division of the seventh joint (as it would be counted in the 

 seventeen- jointed species) into two, thus giving eighteen joints 



70 



