322 BULLETIN- 15 8, UNITED STATES NATIONAL MUSEUM 



Genus CYCLOPS O. F. Muller, 1776 



Metasome moderately widened and more or less depressed, con- 

 siderably narrowed posteriorly; head fused with the fir^t segment; 

 lateral portions of metasome segments produced into angular epimeral 

 plates, giving the margins of that part of the body a jagged appear- 

 ance. Urosome slender; genital segment dilated anteriorly; caudal 

 rami usually much longer than wide. First antennae 17-segmented, 

 the number of segments sometimes reduced by fusion; second an- 

 tennae 4-segmented without an exopod. Mandibular palp replaced 

 by two or three setae; maxillary palp also rudimentary. Rami of 

 first four pairs of legs 3-segmented, those of first and second pairs 

 rarely less; fifth leg S-^segmented, end segment with a long apical 

 seta and a short inner spine. T"wo subcylindrical ovisacs. 



KEY TO THE SPECIES (BOTH SEXES) 



1. Basal segment of fifth leg five times as wide as terminal segment ; 



inner spine of latter extremely short viridis (p. 322) 



Basal segment of fifth leg scarcely twice as wide as terminal 



segment; inner spine of latter long and setose bicuspidatus (p. 324) 



CYCLOPS VIRIDIS (Jurine) 



Figure 192 



Cyclops vulgaris Koch, Deutschlands Crustaceen, Myriapoden und Arachniden, 

 pt. 21, pi. 4, 1838.— Sabs, Crustacea of Norway, vol. 6, p. 40, pi. 22, 1913. 



Occurrence. — Both sexes found in moderate abundance in Salt 

 Pond, Sidleys Pond, Oyster Pond, Flax Pond, and a small lily pond 

 south of Ashumet Pond, all in Falmouth; in a small ice pond and 

 Gosnold Upper Pond on Cuttyhunk Island; in a small pond near 

 Chatham ; in a small pond on Uncatena I,sland ; in Hinckleys Pond, 

 Harwich ; in Jones pond, Waquoit Village ; in Tarpaulin Cove Pond 

 and West End Pond on Naushon Island. 



Distribution. — Germany (Koch) ; Sweden (Lilljeborg) ; British 

 Isles (Brady) ; Russia (Fischer) ; France (Richard) ; central Asia, 

 Siberia, Norway lakes (Sars) ; United States (Marsh, Herrick, 

 Forbes). 



Color. — Very variable; sometimes light olive-gi-ay, with scattered 

 patches of dark brown along the posterior margins of the segments, 

 forming a continuous band at the groove between the first two free 

 thoracic segments. Again the head may be covered on the dorsal 

 surface with small circular red spots, sparsely and irregularly scat- 

 tered. The anterior and posterior end,s of the digestive tract are 

 often brick red while the median portion is blue. Ej^e dark blue; 

 eggs bluish gray. 



Female. — Body stout, metasome broadly oval, the second, third, 

 and fourth segments projecting angularly at the posterior corners, the 



