158 TWELFTH ANNUAL REPORT. 



one margin and bristled on the other; the next seta is as long as 

 the abdomen, being somewhat exceeded by the following one; inner 

 seta as long as the outer, but feeble; upper seta nearly as long, ap- 

 proximated; length less than 1 mm. 



A well marked variety of the above occurs in America, which 

 might rank as a species, were it not probable that it is simply a 

 post-imago form occurring only under favoring circumstances. This 

 variety lias no connection with Brady's var. montauus. 



Cyclops sernilatus, var. elegaus. (Var. u.) 



Distinguished from the type by the greater size, and the elonga- 

 tion of antennae and caudal stylets. We will first of all give the 

 measurements 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 segment of the thorax is long proportionally (0.40 mm.) 

 The antennae are very long, reaching to the base of the third seg- 

 ment (.68 mm.). The egg-sacs are elongate-oval, being more slender 

 ■even than in typical C. serrulatus; in the animal measured they 

 were 0.50 mm. long, by 0.19 mm. wide. The caudal stylets are 

 slightly shorter than the last two segments of the abdomen. The 

 antennules are very short, and each joint has its series of fine teeth. 

 The free lower margins of the thorax are ornamented Avith series 

 of prominenc*, while the last segment is extended into a blunt 

 angle bearing long teeth. The last segment of the abdomen is 

 spiny-margined and is ornamented with a double row of spines at 

 the anus. The armature of the stylets as well as that of the feet is 

 identical with that in typical C. serrulatus. The last two joints of 

 the antennae measure 0.1 mm. each, while the two previous measure 

 unitedly 0.12 mm. The color is not opaque as in the smaller form 

 usually. Brady's var. montanus has shorter stylets than the type, 

 but seems nearest the small dark form found in peaty waters in 

 America. Cyclops pectinifer, Cragin, has no distinctive points, it 

 being typical C. serrulatus. 



Sp. 25. Cyclops macrurus, Sars. 

 Cyclops macruvus, brady. 



Closely allied with C. serrulatus. Cephalothorax ovate, rounded 



