COPEPODS OF THE WOODS HOLE REGION 325 



a convex cover, the sperm canals arising from the rim. Total 

 length, 0.95-1.35 mm. 



Male. — Body much more slender than in the female, four times as 

 long as wide ; cephalic segment one-third longer than the rest of the 

 metasome, the other metasome segments with lateral epimeral plates. 

 Urosome half as long as metasome ; genital segment wider than long ; 

 abdominal segments diminishing in length distally; caudal rami as 

 Jong as the three last segments combined, eight times as long as wide, 

 the inner apical seta less than twice the length of the ramus. 



First antennae 16-segmented, twice geniculate, the middle section 

 scarcely swollen, the terminal section 3-segmented and nearly as long 

 as the middle section; when reflexed these antennae reach the mid- 

 dle of the fourth metasome segment. The second antennae, mouth 

 parts, and five pairs of legs are like those of the female; the two 

 setae on the fifth legs are slender and very elongate, especially the 

 apical one. There is a pair of rudimentary sixth legs at the poste- 

 rior corners of the genital segment, each consisting of a short, la- 

 mella armed with three setae, the outer one slender and elongate, 

 the inner one shorter and broader, the middle one still shorter and 

 nonf)lumose. Total length, 0.75-1 mm. 



Remarks. — Birge and Juday have noted that in certain Wisconsin 

 lakes this species is found during summer in a resting stage, in- 

 closed in a cocoon of mud from which the copepod emerges in au- 

 tumn. It is a common limnetic form of the Great Lakes, according 

 to Marsh, and may be recognized by the position of the outer seta 

 on the caudal rami, the elongated form of the rami themselves, and 

 the 17-segmented first antennae. 



Genus MICROCYCLOPS Claus, 1893 



Body cycloi3oid; metasome elliptical, twice as long as wide, fifth 

 segment somewhat produced laterally; head fused with first seg- 

 ment. Urosome slender ; genital segment scarcely dilated anteriorly ; 

 caudal rami longer than wide. First antennae 11- or 12-segmented ; 

 second antennae 4-segmented, without an exopod. Rami of first four 

 pairs of legs 2-segmented, terminal segments much longer than the 

 basal; fifth leg apparently 1-segmented, its basal segment entirely 

 fused with the fifth metasome segment and represented by a lateral 

 seta on the margin of the latter; terminal segment conical with a 

 single apical seta, and sometimes an almost invisible inner spine. 

 Two ovisacs; eggs large and few in number, 



KEY TO THE SPECIES (BOTH SEXES) 



1. First antennae 12-segmented ; caudal setae very unequal and 



one-half longer than the urosome varicans (p. 326) 



First antennae 11-segmented ; caudal setae subequal and a little 



shorter than the urosome ,„ — . — ^_^_^_._— ._. bicolor (p. 327); 



