ENTOMOSTRACA OF MINNESOTA. 147 



sexual openiogs just behind the hist pair of feet. It is the upper or 

 longer branch of the antennae which in Sida is three-jointed, while the 

 reverse is the case in the next genus. The only species, according to 

 P. E. Mueller, is the ubiquitous 



* Sida crystallina. 



Plates XXXV, Figs. 13-15; XXXVII, Figs. 1, 2. 



P. E. Mueller (Daphne crystallina); Latreille (Daphnia crystallina); Straus; Milne- 

 Edwards '34-40; Gmelin, Manuel, Fabrioius (Monoculus crystal) inus) ; De Geer 

 1778 (Monoculus elongatus); Lievin '48; Baird '50; Lilljeborg '53; Fischer; 

 Schoedler'58and '63; Leydig '60; Sais '65 (elongata, and crystallina; P. E. Mueller 

 '68; Kurz '74; Birge '78; Herrick '79, '82 and '84; Lutz '79; Weismann; 

 Grobben '79. 



The S. elongata of Sars is distinguished by the smaller head and its 

 concave lower margin and more elongate shell. The terminal joint of 

 the longer ramus has one less seta than S. cri/stallina, while the post- 

 abdomen has more numerous spines. We incline to believe it a valid 

 variety at least. 



GENUS PSEUDO-SIDA Herrick. 



Similar to Sida. Antennules of the female with a long flagellum, 

 like that of the male of Sida, sensory setse lateral. Body elongate, 

 head short, extending into a sharp beak. The post- abdomen is armed 

 with groups of sharp spines or bristles. Most characteristic, how- 

 ever, is the fact that the antennary joint, which in Sida is two jointed, 

 in this species is tri-articulate, and the two-jointed ramus has a great 

 number of setae (16 to 17). 



*Pseu(lo-sida tridenta Herrick. 



Plates XXXVI, Figs. 2-6; L, Fig. 9. 



Herrick '84 (bidentata. By oversight the number of caudal teeth was misstated and 

 the name made to correspond.) and '87. 



Head very short, acute below, the beak bearing in the female a 

 pair of rather large antennules which are armed with a pectinate pro- 

 cess three times the length of the antennule, and a cluster of about 

 five sensory setae. The antennae are as long as in Sidasmd well armed. 

 The basal joint of the two jointed branch bears seven setae, the second 

 ten setae of which two are apical; three jointed ramus with very short 

 basal segment, second four times as long as wide and armed at the end 

 with two setae and a spine; third segment very small, with three setae 

 and a minute spine. The maxilla is two-jointed, the terminal joint 

 bearing nine jointed spines or short setae. The first foot of the adult 

 10 



