152 TWELFTH ANNUAL REPORT. 



quadrate, broad, and bearing one long spine. The second joint is 

 narrow and longer, parallel and truncate, with one terminal spine 

 about equal to the preceding, and one about half that length. 



From C. hicuspidatus, Claus, this species may be distinguished 

 by the armature of the outer ramus of the first pair of legs, and 

 from C. bisetosus^ Rehberg, by the armature of the outer rami of 

 the other legs. 



It shares with Diaptomus sicilis the responsibility of affording 

 to the young white-fish their earliest food." 



(16 c) Cyclops insectus, Forbes. 



(Plate U. Fig. 9.) 



"Closely allied to the preceding, but more robust in all its parts, 

 and with the second cephalothoracic segment widest. The abdo- 

 minal segments are all bordered with spinules posteriorly. The 

 two median caudal setae are much more nearly equal than in tho- 

 masi^ the outer and the inner are very short, but longer than in 

 that species. The inner in our specimens is longer than the outer 

 — the reverse being the case in hicusp>idatus as described by Claus. 



*'The legs are armed nearly as in thomasi^ but the last joint of 

 the outer ramus of the first pair has two spines externally besides 

 the one at the tip, and the terminal spines on the last segment of 

 the inner ramus of the fourth pair of legs are about equal." 



Both forms probably occur in Minnesota, though the second has 

 been seen but once, and the identification lacks confirmation. The 

 diff'erences between the two are almost exactly those prevailing 

 between C. hicuspidatus (= pulchellus) and C. bisetosus, Reh., if 

 I correctly understand Sars. Claus" description does not agree 

 with that of Sars. Further study of the European types will be 

 necessary before a satisfactory settlement can be reached. 



(16 b) Cyclops navus, Herrick. 



Cyclops navus, herrick, Copepoda of Minnesota, p. 279. 



This name, proposed at nearly the same time as C. thomasi, ap- 

 plies to a very closely related form which I can but regard as a 

 variety of that species. It seems constant in its differential char- 

 racters in given localities, but we are now familiar enough with 

 the fact that changed conditions in the water occasion changes in 

 forms in the copepods. 



This form inhabits shallow pools. It is larger than C. thomasi, 



