North American Species of Diaptomus. 105 



pair of feet, which in the male never assist in 

 copulation ; on the contrary, the male attaches the 

 spermatophores directly to the vulva of the female 

 without the help of appendages. Genital organs of 

 the male generally paired, the openings always sym- 

 metrical. Pulsating dorsal vessel almost always 

 absent. The female carries the eggs w T ith her, gener- 

 ally cemented into one or two egg sacs, until emer- 

 gence of the young. 



Suborder II. PODOPLEA. 



Diaptomus Westwood. 



Cyclops, O. F. Miiller, 17S5. 

 Monoculus, Jurine, *20. 

 Diaptomus, Westwood, '36. 

 Cyclopsina, Milne-Edwards. ";58. 

 Glaucea, Koch, 'So- 41 

 Cyclops, Xicolet, '48-49. 



" Cephalothorax always with seven segments, of which the 

 anterior two, indistinctly confluent, form the head. The last 

 thoracic segment in the female rather large, posteriorly deeply 

 emarginate in the middle, and often produced laterally on 

 both sides into a biangulate lamina. Abdomen short, nar- 

 rower than the thorax ; in female of four segments (caudal 

 rami included), of which the first is dilated anteriorly and 

 very often armed with a lateral spine on each side ; in male 

 composed of six obvious segments of about equal width. 

 Caudal rami with five uniarticulate plumose setae and with 

 another much smaller, more slender seta within. The front 

 provided with two minute tentaculiform appendages. The 

 first pair of antennas composed of 25 segments, increasing 

 slightly in length toward the tip. The geniculate articulation 

 between the 18th and 19th segments of the right male 

 antenna ; the six preceding segments swollen, the five following 

 sometimes confluent into two articles. The outer ramus of 

 the second pair of antennas 7 -jointed, longer than the inner 

 ramus, the last article longest of all and armed with very 

 long apical seta? ; setse of preceding articles short and 



