BYRNES: CYCLOPS OF FRESH WA lER. 7 



one on the apex and one on the outer angle. The posterior mar- 

 gins, dorsal and ventral, of the last abdominal segment are serrated. 

 The stylets are armed with four plumose setae and two short hairs, 

 often without barbs. While not a profusely hairy form, hairs are 

 often present on the rami of the swimming feet of this species, 

 particularly on the outer margins of the segments of the inner 

 rami. The margins of the segments are often strongly serrated as 

 well as hairy. 



Herrick's notes on C. ater are very brief. He describes ater as 

 "our most characteristic American species ; color deep blue or gray ; 

 ovisacs pale." He also finds young with "a deep band of color 

 crossing the thorax near the middle", but makes no mention of the 

 color of the ovaries which is so striking that, had he observed it, 

 he could hardly have failed to mention the fact in his writings. 



Professor Marsh quotes Professor Reighard's description of C. 

 ater with which the banded form from Cold Spring Harbor agrees 

 very closely. He also observed the orange colored ovaries. 



In the proportion of parts and in the armature of the appendages, 

 the two forms agree ; but, as in the case of C. serrulatns, the sig- 

 nificance of the occurrence of differently colored ovaries with a 

 uniformly different distribution of pigment needs further study. 

 Without further acquaintance with the two forms, the differences 

 are sufficiently striking to suggest that they might be well marked 

 varieties. 



Variations of C. Atcr.—T\\& Cold Spring Harb<:)r forms of ater 

 present little variation in their armature. They differ, however, 

 from the forms described by Professor Herrick, who found the 

 "setae all short and stout," whereas the setae are quite long and well 

 formed in the ater found at Cold Spring Harbor. They differ 

 also from the forms described by Professor Marsh in that they 

 have a well formed spine in the apical position on the outer ramus 

 of the first foot, where Professor Marsh finds a seta. This outer 

 "seta" on the apex of the outer ramus of the first foot is, as Fig. 

 6, Plate I., shows, clearly a well formed seta on the median side 

 and a spine on the outer margin. This shows that set;e and 

 spines are interchangeable and hence can be accorded little value 

 in the determining of species. 



As for the fifth foot, the Cold Spring Harbor forms of C. ater 



