8 COLD SPRING HARIJOR MONOGRAPHS. VII. 



agree with Professor Marsh's account in having a strong spine 

 on the inner angle and two setse, one median and one on the outer 

 angle. The median seta reaches to the posterior margin of the 

 first abdominal segment. The setae may or may not be without 

 hairs. Herrick observed "three subequal spines" on the distal 

 margin of the fifth foot. 



Cyclops ater is one of the largest Cyclops seen in the Long Island 

 waters. It represents a very well marked species, in which there 

 appears to be but very little variation. 



Associated with C. atcr is a little water mite belonging to (he 

 genus Arrhenurus. This fact was observed by Professor Marsh 

 in 1895 and I also have observed this Arrhenurus. It was first 

 called to my attention by the fact that it and C. ater resemble each 

 other not only in size and color, but also in their manner of 

 movement. C. ater does not dart through the water as do many of 

 the Cyclops, but potters about with short jerk movements, thus 

 greatly increasing its resemblance to the accompanying form. Fur- 

 ther observation showed, however, that the water mites are not 

 always dark like the Cyclops ; sometimes they are mottled and some- 

 times bright red. 



Cyclops Signatiis, Koch, 



General Description. — Cyclops signatiis is one of the largest 

 and most abundant species found at Cold Spring Harbor, attain- 

 ing and often exceeding a length of 1.5 mm. The species is 

 represented by two forms — coronatus and aiiniilicornis — which 

 occur side by side and closely resemble each other. The presence 

 of these two forms with their transitional stages in the same locality 

 offers not a little difficulty to the student who is unacquainted with 

 the varietal characteristics of the species. 



The species can readily be identified even in early stages by the 

 presence of a two- jointed fifth foot, in which the outer basal seg- 

 ment bears on its outer angle, a seta without barbs or with barbs, 

 according to age; and in which the distal segment bears a median 

 seta and two lateral spines also with or without serrations according 

 to age. 



The antenuce in the adults contain seventeen segments and reach 

 to the abdomen. The armature of these segments is extremely 



