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. LXXYII, 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. LXXYII, fig. 3). The last three 

 antennal segments bear a lateral hyaline plate (PI. LXXYII, 

 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 albidus these hyaline plates in some cases extend back upon 

 the preceding segments. I find, as does Schmeil, contrary to 

 the statement of Yosseler, 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 albidus. (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. Yosseler gives it, however, as I 

 have found it. 



A structure not mentioned by any of the European authors 



