28 COLD SPRING HARBOR MONOGRAPHS. VII. 



Herrick records an outer spine instead of a seta on the inner- 

 ramus in the third and fourth feet. As all the forms I have exam- 

 ined agree in the armature, this variation is probably more or 

 less constant in the forms from the two localities, i. e., west and 

 east. 



It is very characteristic of C. scrriilatus that the first pair of 

 swimming feet is disproportionately small in comparison with the 

 corresponding feet of other species. This fact often afifords a ready 

 means of immediate recognition. 



I attempted to rear the young of C. semilatus to determine the 

 significance of the different colors of the ova in the two types, but 

 I have as yet no light to throw on the relationship of these forms. 



Cyclops Fluviatilis, Herrick (Plate XV., Figs, i and 2). 



This species, as found by me on Long Island, is so small as to 

 be easily overlooked. Under the microscope it is, however, recog- 

 nized with facility by its color markings. The cuticula is yellow 

 and strongly splotched with dull bluish-green patches rather irregu- 

 larl}^ scattered over the body. Herrick* (1895, p. 114) speaks of 

 "a smaller age form which is barely visible to the eye," and of a 

 "larger and more highly colored condition." Only the smaller 

 form has been seen in the Long Island waters. It is, however, 

 sexually mature as is indicated by the enlarged first segment of the 

 abdomen, by ova within the body and by appended embryos wdiich, 

 though few in number are of relatively large size. 



C. fliiviatilis was abundant in the collections made in the summer 

 of 1905, at Cold Spring Harbor, though I had not encountered it 

 there previously. 



The Cold Spring Harbor form agrees very closely with Herrick's 

 description. The antenn?e reach about to the abdomen and contain 

 greatly elongated segments, from the seventh to the ninth, as 

 Herrick pointed out. 



The swimming feet are likewise armed with very long set?e. The 

 armature of the terminal segment of the swimming feet is as 

 follows : 



* "Copepoda, Cladocera and Ostracoda of Minnesota." Geological and 

 Natural History Survey of Minnesota. 1895. 



