112 GEOL. AND NAT. HIST. SURVEY 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 antennz. 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: 
First FEET. 
ex. 3 spines. ex. 1 seta. 
‘Outer ramus |S 2 sete. Inner ramus {eo 1 spine, 1 seta. 
in. 3 sete. in. 3 sete. 
SECOND AND THIRD FEET. 
ex. 3 spines. ex. 1 spine. 
‘Outer ramus 4 ap. 1 spine, 1 seta. Inner ramus +ap. 1 spine, 1 seta. 
in. 4 sete. in. 3 sete. 
FouRTH Foot. 
ex. 2 spines. ex. 1 seta. 
Outer ramus |" 1 spine, 1 seta. Inner ramus | 2 spines. 
in. 4 sete. in. 2 sete. 
The spines of the feet are strongly serrate and the sete 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., antenne 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. 
Distingnished from the type by the greater size, and the elongation 
of antenn 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 antenne 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- 
eal C. 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 
