Marsh—North American Species of Diaptomus. 441 
DIAPTOMUS TYKELLI Poppe. 
Plate XIX, figs. 2, 3, 8. 
1888. Diaptomus Tyrelli Poppe, p. 159. 
1889. Diaptomus Tyrelli DeGuerne and Richard, p. 39; pi. I, 
figs. 17, 18; pi. IV, fig. 26. 
1895. Diaptomus Tyrelli Herrick and Turner, p. 76; pi. X, 
fig. 9. 
1897. Diaptomus Tyrelli Schacht, p. 176. 
Of medium size. The suture of the first cephalothoracic 
segment is rather distinct. The first segment is considerably 
less in length than the three following. The last cephalotho¬ 
racic segment is expanded into large lateral processes, and is 
armed with rather large lateral spines. 
The first segment of the female abdomen equals in length 
the rest of the abdomen. It is broad, dilated in front, and 
moderately dilated laterally. It hears prominent lateral proc¬ 
esses, which are tipped with acute spines. The second seg¬ 
ment is shorter than the third, and the two together are some¬ 
what longer than the furca. The furcal rami are stout and 
ciliate on both the inner and the outer margins. 
The antennae are 25-segmented and reach about to the end 
of the furca. The antepenultimate segment of the right male 
antenna is without any special appendage. 
The fifth feet of the female are slender. The spines of the 
first basal segments are small and acute. The lateral hair of 
the second basal segment is of moderate length. The first seg¬ 
ment of the exopodite is more than twice as long as wide. The 
second segment is long and slender, exceeding in length the 
first segment. The hook is slightly curved and denticulate on 
the inner margin. It is armed with three spines of which the 
inner is the longest. The two inner spines represent the third 
segment. The endopodite is long and slender, exceeding in 
length the first segment of the exopodite. It is setose at the 
tip, and armed with two long terminal spines which are insert¬ 
ed well back from the end of the endopodite. 
