104 Illinois State Laboratory of Natwral History. 



joint of the outer ramus ; those of the male with the 

 inner ramus 3- jointed and provided with plumose 

 hairs, as in the other legs. 



14 (15). Fifth pair of legs of female with the inner hairs of the 



last joint of the outer ramus transformed into short 

 thick spines. In the male, outer ramus of left leg of 

 fifth pair with two joints ; outer ramus of right leg with 

 three. Genus Osphranticum. 



15 (14). Fifth pair of legs of female with the inner hairs of 



the last joint of the outer ramus long and plumose. 

 Fifth pair of legs of male with both outer rami 2- jointed. 



Genus Limnocalanus. 



16 (9, 17). Abdomen of female 4-jointed, symmetrical. 



Antennas 25-jointed, articles 24 and 25 not confluent. 

 Four anterior pairs of feet generally with 3-segmented 

 rami, the fifth with 3-segmented outer and 2- or 3-seg- 

 mented inner ramus. Male antenme with segments 

 19-21 and 21-23 confluent. Fifth pair of feet sub- 

 chelate ; the right with 2-, the left with 3-segmented 

 rami. Subfamily Leuckartiixa. 



17 (9,16). Abdomen 3- or 4-jointed, not always symmetrical. 



Four anterior pairs of feet with 3-jointed rami. Gen- 

 erally the left antenna of the male geniculate. Articles 

 19-21, 22 and 23 (or 22-25), and 1 and 2 confluent. 

 Fifth pair of legs with 3-segmented outer and 1-3- 

 segmented inner rami. ChelaB undeveloped or want- 

 ing. Subfamily Heteroch.etixa. 



18 (4). Rostrum wanting. Fourth and fifth thoracic segments 



of female not confluent. Abdomen 3-segmented. Male 

 genital opening on the left ; right antenna prehensile, 

 segments 17 and 18, and 19 and 20 confluent. Inner 

 rami of fifth pair of feet wanting; outer ramus of left 

 foot 4-segmented, of right foot 3-segmented. Marine. 



Family C'axdacid.e. 



19 (1). Division of body into anterior and posterior parts in 



front of the last (fifth) thoracic segment. This bears, 

 almost without exception, a more or less rudimentary 



