414 
Wisconsin Academy of Sciences, Arts , and Letters. 
DIAPTOMUS MISSISSIPPIENSIS Marsh. 
Plate XY, figs. 3, 5, 8. 
1894. Diaptomus mississippiensis Marsh, p. 15; pi. I, figs., 
1-3. 
1895. Diaptomus mississippiensis Herrick and Turner, p. 78;.. 
pi. XLVII, figs. 1-3. 
1897. Diaptomus mississippiensis Schacht, p. 173; pL 
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 ordinarily 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 length of the first segment of the exopodite. It is setose at 
tip and bears two terminal spines. 
