102 Illinois State Laboratory of Natural History. 



SYNOPSIS OF THE RELATIONSHIPS OF THE GENERA Os]>h f(l liticiim, 



Limnocalanus, Diaptomus, and Epischwra, 

 of the family C entropagidce . 



(Adapted and compiled from Giesbrecht ('92), and from manuscript 

 of Prof. S. A. Forbes.) 



1 (19). Division of body into cephalothorax and abdomen 



between the thoracic segment bearing the fifth pair 

 of feet and the segment bearing the genital apertures. 

 In the male the fifth pair of feet assists in copulation. 

 Abdomen with five segments ; without appendages. 

 Genital organs of the male unsymmetrical. Pulsating 

 dorsal vessel generally present. Female deposits eggs 

 singly or carries them with her in single sac until emer- 

 gence of the nauplii. Suborder I. GYMNOPLEA. 



2 (3). Anterior antennae of male symmetrical or nearly so, 



and more richly provided with sense-clubs [cesthctasks] 

 than those of the female. Fifth pair of feet of female 

 either normal, or degenerate to complete disappear- 

 ance. Secondary sexual distinctions of male not con- 

 fined to peculiarities in the structure of the body, the 

 antennae, the fifth pair of feet, and the segmentation of 

 the abdomen, but usually present in the cephalic 

 appendages and sometimes also in the swimming feet. 

 Marine. Tribe I. Amphaskandria. 



3 (2). Anterior antennae of male unsymmetrical. Fifth pair 



of feet in the female either normal or degenerated, but 

 never absent. Secondary sexual characters of male 

 generally confined to peculiarities in the structure of the 

 body, the antennae, and the fifth pair of feet. Marine 

 and fresh- water. Tribe II. Heterarthrandria. 



4 (18). Eostrum present. Fourth and fifth thoracic seg- 



ments confluent. 

 5(6). Abdomen of female 1-3-segmented. Antennae 16-24- 

 jointed ; last two segments always confluent. In the 

 male the fifth pair of feet rarely with a rudimentary 

 inner ramus. Antenna 1 with segments 19-21 and 

 sometimes 22-25 confluent. Marine. 



Family Pontellid^:. 



