1074 Wisconsin Academy of Sciences, Arts, and Letters. 



1909. Cy .lop: americanus Byrnes, p. 13, pi. V, figs. 1-3. 



1909. " parens Byrnes, p. 14, pi. VI, figs. 1-8, pi, X. figs. 1-3. 



1909. " brevispinoxux Byrnes, p. 16, pi. VII, figs. 1-!). 



1909. " mgens Byrnes, p. 22, pi. VIII. tigs. 1-4. 



Cephalothorax oval, its breadth rather more than one- 

 half its length. The cephalothorax is about twice as long as 

 the abdomen exclusive of the jfurcal rami. Each cephalo- 

 thoracic segment projects beyond the one following it. 



The anterior part of the first abdominal segment is larger 

 than the posterior, but this difference is not so marked as in 

 some other species. The posterior margins of all the ab- 

 dominal segments except the last are serrate, — the last seg- 

 ment is armed with small spines; this armature of the ab- 

 dominal segments is more marked in the immature forms. 



The furcal rami are very variable in length. They may be 

 scarcely longer than the last abdominal segment or they may 

 be four times as long. In some varieties the rami are ciliate 

 on the inner margins. The lateral seta of the furca is com- 

 monly well towards the distal end, varying in position from 

 two-thirds to four-fifths the length of the ramus. Of the 

 terminal armature of the furca, the outermost is very variable ; 

 it may be a slender plumose seta, or it may be a short, blunt 

 spine. It is never, however, very much elongated. 



The first antennae are 17-segmented and reach to or a lit- 

 tle beyond the posterior margin of the first cephalothoracic 

 segment. The twelfth segment has a club-shaped sense hair. 



The spinous armament of the terminal segments of the 

 exopodites of the swimming feet may be 2, 3, 3, 3, or 3, 4, 4, 4. 

 The terminal segment of the endopodite of the fourth foot 

 may have exteriorly either a seta or a spine. 



The fifth foot, Plate LXXII, figs. 7 and 8 consists of two seg- 

 ments. The first segment is broad, its breadth ordinarily 

 equalling or exceeding its length ; on its inner distal segment 

 it bears a long plumose seta. The second segment is of about 

 the same length as the first segment, while its width is one- 

 half or less than that of the first segment; on its distal end 

 near the outer margin is a long plumose seta, at the inne* 



