48 PROCEEDINGS OF THE ACADEMY OF [Jail., 



the stylets. The first pair of antennae are a brownish-yellow; their 

 anterior border is often tinged with green. Forbes has "seen both 

 blue and pink individuals." Herrick found that the color varies 

 "from deep indigo to greenish-brown." Cragin states: "Animal 

 dirty blue-green, antennae lighter. Dark green pigment masses are 

 scattered beneath the integument in various places, particularly 

 along the anterior side of the first antennae." 



This species is quite generally distributed over the eastern and 

 central United States. Herrick found it in Lake Minnetonka, Minn. 

 Marsh reports the species from Lake Erie, Lake Michigan, and some 

 of the smaller lakes of Michigan and Wisconsin. Forbes has found 

 it in collections from Sister Lake, Fla., and many localities in the 

 State of Illinois. As C. fluviatilis Herrick, Brewer reports it from 

 the vicinity of Lincoln, Nebraska, and Miss Byrnes from Long 

 Island. Miss E. R. Walker reports it as the most abundant form 

 from Todd's Pond, Oregon. It is one of the most abundant forms 

 in September and October dredgings, but I have noted only a few 

 individuals during the winter months. 



It is easily distinguished by its small size, its habit of swimming 

 near the surface, its dark color (it frequently appears to be black 

 to the naked eye), and, under the microscope, by the very charac- 

 teristic form of the receptaculum seminis and short caudal setae. 



Subgenus PARACYCLOPS Claus. 

 ■Cyclops phaleratus Koch. PI. IV, figs. 1-4. 



Cyclops phaleratus Koch, '35-'41, Heft 21, pp. 8, 9, pi. IX. 



Cyclops pcrarmatus Cragin, '83, pp. 72, 73, pi. I, figs. 9-18. 



Cyclops phaleratus Schmeil, '92, pp. 170-178, pi. VIII, figs. 1-11. 



Cyclops phaleratus Herrick and Turner, '9.5, pp. 120, 121, pi. XMI, figs. 1-7; 



pi. XVIII, figs. 2-2d; pi. XIX, fig. 1; pi. XXI, figs. 6-10. 

 Cyclops phaleratus Marsh, '95, pp. 19, 20. 

 Cyclops phaleratus Forbes, '97, pp. 59-62, pi. XX, fig. 3. 

 Cyclops phaleratus Lilljeborg, '01, pp. 10.5-109, pi. VI, figs. 20, 21. 

 Cyclops phaleratus Byrnes, '09, pp. 31-33, pi. XIV, figs. 1-9. 



Specific Description. — The first segment of the unusually broad 

 cephalothorax is a little longer than the other four thoracic segments. 

 Its width is slightly greater than its length. The posterior borders 

 of the first three thoracic segments are smooth. The fourth segment 

 is ornamented with a minute fringe of short serrations. The chitinous 

 covering of the fifth thoracic segment is compo.sed of a continuous 

 cylinder like the abdominal segments, and not of a dorsal and ventral 

 plate, as is the case in the corresponding segment of other species of 

 this genus. This segment is armed ventrally along its posterior 

 margin by a row of heavy, cone-shaped teeth (PI. IV, fig. 4) which 



