Marsh—North American Species of Cyclops . 1091 
length and the cephalothorax compares in length with the ab¬ 
domen as seven to four. The posterior angles of the segments 
of the cephalothorax are not especially prominent. The first 
segment is about three-fourths of the length of the whole 
cephalothorax. 
The first abdominal segment (PI. LXXVII, fig. 1) is only 
slightly enlarged at its proximal end. Its length is rather less 
than the combined length of the three following segments. The 
last segment is armed on its posterior border with small spines. 
The furcal rami are twice as long as wide, and ciliated on 
their internal margins. The lateral seta is near the distal 
end. Of the four terminal setae both the outer and the inner 
are elongated. The inner is seldom more than twice the 
length of the outer. All the terminal setae are strongly plu¬ 
mose. 
The first antennae are composed of seventeen segments, and 
reach to the end of the cephalothorax. The twelfth segment 
bears a sensory hair. The eighth, ninth, tenth, twelfth, thir¬ 
teenth and fourteenth segments have rows of large spines on 
their posterior borders (PI. LXXVII, fig. 3). The last three 
antennal segments bear a lateral hyaline plate (PI. LXXVII, 
fig. 4). In the last segment this hyaline plate is deeply notched 
on the first two-thirds of the segment, having four especially 
deep notches. The latter third of the plate is finely serrate. As 
in alhidus these hyaline plates in some cases extend back upon 
the preceding segments. I find, as does Schmeil, contrary to 
the statement of Vosseler, that the indentations in the mem¬ 
brane of the last segment do not disappear in mounted speci¬ 
mens, but remain permanently like other cuticular structures. 
In the second antennae, the inner margins of the first three 
segments are setose. The second segment is short and the 
third very long as compared with the corresponding structures 
in alhidus. (PI. LXXVII, fig. 5.) 
The spinous armature of the swimming feet is 4, 4, 4, 3. 
This is as I have found it in all my American specimens. 
Schmeil gives it 3, 4, 4, 3. Vosseler gives it, however, as I 
have found it. 
A structure not mentioned by any of the European authors 
