414 Wisconsin Academy of Sciences, Arts, and Letters. 



DiAPTOMus MississippiENSis Marsh. 

 Plate XV, figs. 3, 5, 8. 



1894. Diaptonuis mississippiensis Marsh, -p. 15 ; pi. I, figs. 



1-3. 



1895. Diaptomus mississippiensis Herrick and Tiirner, p. 78 ; 



pi. XLVII, figs. 1-3. 

 1897. Diaptomiw mississippiensis Scliacht, p. 173; pi. 

 XXXIII, figs. 1-4. 



Of moderate size. The suture of the first cephalothoracic 

 segment is very distinct. This segment is about equal in length 

 to the three following. The last cephalothoracic segment is 

 armed on each side with a minute spine. 



The first abdominal segment of the female is as long as the 

 remainder of the abdomen and the furca. It is dilated later- 

 ally and in front, and bears two lateral spines of which the 

 right one is ordinarilj' somewhat the larger. The second seg- 

 ment is somewhat shorter than the third, and the third and the 

 furca are about equal in length. The length of the furcal rami 

 considerably exceeds their width, and they are ciliate on the 

 inner margin. The furcal setae are short and stout. 



The antennae are 25-segmented and reach beyond the furca. 

 The right antenna of the male is much swollen anterior to the 

 geniculating joint; the antepenultimate segment has no append- 

 age. 



The female fifth feet are rather short and stout. The spines 

 of the first basal segments are small. The lateral hairs of the 

 second basal segments are moderately long. The length of the 

 first segment of the exopodite is less than twice its width. The 

 hook of the second segment is short, acuminate and slightly 

 curved. It is denticulate on the inner margin. The third 

 segment is represented by two spines, of which the inner is the 

 longer. The endopodite is one-segmented and slightly exceeds 

 the leng-th of the fii-st segment of the exopodite. It is setose at 

 tip and bears two terminal spines. 



