112 GEOL. AND NAT. HIST. SUEYEY OF MINNESOTA. 



cephalic margin of the last thoracic segment, tending to assume dur- 

 ing life the form of a rude Z, the proximal four joints forming the 

 base; the last three joints are slender and elongate and are each armed 

 with a hyaline plate. Antennules small, reaching about the sixth 

 joint of the antennae. Jaws small, with large teeth. Caudal stylets 

 over four times as long as wide, nearly as long as the last two abdom- 

 inal segments, serrate down the outer margin. Outer apical seta 

 changed to a very strong and serrate spine, inner seta weak, outer 

 median seta over two-thirds as long as the inner. Formula for the 

 armature of the feet as follows: 



FiKST Feet. 



!ex. 3 spines. ( ex. 1 seta, 



ap. 2 setfe. Inner ramus I ap. 1 spine, 1 seta: 



in. 3 setae. I in. 3 setae. 



Second and Third Feet. 



(ex. 3 spines. ( ex. 1 spine, 



ap. 1 spine, 1 seta. Inner ramus < ap. 1 spine, 1 seta, 



in. 4 setae. (.in. 3 setae. 



Fourth Foot. 



!ex. 2 spines. Tex. 1 seta, 



ap. 1 spine, 1 seta. Inner ramus < ap. 2 spines, 



in. 4 setae. (.in. 2 setae. 



The spines of the feet are strongly serrate and the sette fully pec- 

 tinate. The fifth foot is one jointed, having one very strong serrated 

 spine, an apical seta and a longer inner seta. The adjacent margins 

 of the fifth segment are serrate. Egg sacs oval, as long as the abdo- 

 men, divaricate. Eggs few, dark. Length inclusive of stylets 1.5 

 mm., thorax 0.62 mm., first segment 0.32 mm., abdomen 0.42 mm., 

 stylets 0.11 mm., longest seta 5.0 mm., antennae 0.5 mm. Color 

 rather opaque. A pelagic form or variety has been distinguished, 

 but it must not be confused with var. montanus of Brady. 



* Cyclops serrulatus var. elegans Herrick. 



Distinguished from the type by the greater size, and the elongation 

 of antennaj and caudal stylets. We will first of all give the measure- 

 ments which afford a criterion for judging of the form and proportions. 



Total length 1.34 mm., thorax 0.76 mm., abdomen 0.40 mm., stylets 

 0.18 mm., greatest width 0.42 mm., inner median caudal seta 0.60 

 mm., outer median seta 0.36 mm., inner seta 0.08 mm. The first seg- 

 ment of the thorax is long proportionally (0.40 mm.). The antennte are 

 very long, reaching beyond the base of the third segment (0.68 mm.). 

 The egg-sacs are elongate-oval, being more slender even than in typi- 

 cal G. serrulatus; in the animal measured they were 0.50 mm. long by 

 0.19 mm, wide. The caudal stylets are slightly longer than the last 

 two segments of the abdomen. The antennules are very short, and 



