Marsh — North American Species of Cyclops. 1083 



lateral hyaline lamella. The lamella on the seventeenth seg- 

 ment is serrate on its margin, and has besides either a single 

 deep depression near its distal end, or four or five such de- 

 pressions. The figure (PI. LXXIV, fig. 10) shows a common 

 form. I do not find, in our American forms the spines spoken 

 of by Schmeil on the antennal segments. 



The segments of the second antenna (PI. LXXV, fig. 3) are 

 elongated. The lower margin of the second segment of the 

 outer maxillipede always has a number of shallow depressions, 

 giving it a more or less crenulated appearance. This appear- 

 ance is described by the German authors under the term ge- 

 ■perlte. While, in some of our forms, this term could be prop- 

 erly applied, more frequently crenulated would describe the ap- 

 pearance more accurately. The figures (PI. LXXIY, figs. 4, 

 5, 6) show the extreme forms as they occur in America. In one 

 (PL LXXIV, fig. 4) this appearance is confined to only a small 

 part of the margin, but is there very distinct, while in the other 

 (PI. LXXIV, fig. 6) it is not so marked but extends through 

 the greater part of the length of the margin. PL LXXIV, fig. 

 5 shows another form intermediate between the others. 



The second segment of the inner maxillipede has on ith 

 anterior margin a number of scattered and rather long setae 

 (PL LXXIV, fig. 11). This seems to be a constant character- 

 istic of this species ; I think it was first mentioned by Brady 

 (Brady 1891) in his description of Scourfeldi. It is not men- 

 tioned by Schmeil but it is shown in his figure of the inner max- 

 illipede. 



The spinous armature of the terminal segments of the ex- 

 opodites of the swimming feet is represented by the formula, 

 2, 3, 3, 3. The membrane connecting the feet of the fourth 

 pair is armed on the posterior border with two blunt spines. 

 (PI. LXXV, fig. 1.) Each segment of the rami is armed on 

 the distal border with a row of spines. 



The fifth feet (PI. LXXIV, figs. 8, 9) are two-segmented. 

 The first segment is short and broad and bears upon its distal 

 outer angle a plumose seta; this seta is ordinarily long as in 

 PL LXXIV, fig. 9, but sometimes it is quite short, as in PL 

 LXXrV, fig. 8. The second segment bears a long plumose seta 



