Geriodaphnm quadrangula — Daplinia pulex. 295 



Ceriodaphnia lacustris is perhaps most closely allied to C. ham- 

 <xta, Sars (90, p. 36). That species has a similar form and habitat, 

 but differs in the shape of the fornices, which are produced " in 

 spinam procurvatam, hamiformem, sat prominentem. " G. 

 hamata also lacks the spines on the head. G. punctata, P. 

 IC.- Mueller is also a pelagic species, and agrees with C. lacustris 

 in the structure of the head and perhaps in that of the post- 

 abdomen. The antennules, however, are far longer in G punc- 

 tata, and the fornices are much smaller. C. pelagica, Tmhof 

 should also be a similar species but I have not been able to 

 refer to Imhof's description. 



Ceriodaphnia quadrangula, O. F. Mueller. 



Sars' account of this species ('90, p. 36.) led me to look 

 carefully over my material from northern Wisconsin with refer- 

 ence to it. I conclude that the species is present. I find how- 

 ever, no really trustworthy figures of the species, and it is very 

 difficult to identify it from the conflicting descriptions of vari- 

 ous authors. Unquestionably more than one form has been de- 

 scribed under this name. There is clearly a form without a 

 pecten on the caudal claw and with no angle in front of the an- 

 tennule, and another similar but with such an angle. I have 

 called the first form C. quadrangula and the second C. pul- 

 chella, but am not sure of my identifications. 



Daphnia pulex, var. pulicaria, Forbes. 



Plate XII, Figs. 1, 2, 3, 4, 5. 



A pelagic species of Daphnia, found in several localities, 

 seems to belong to this variety, described by Forbes ('93, p. 

 242, pi. XXXVII, fig. 1). This species agrees \n general with 

 ■D. pulex, but is transparent and is found in the open water of 

 of lakes and not in muddy pools. A species very close to it is 

 present in temporary pools at Madison. This also differs in 

 color from the typical D. pulex. Although dirty it lacks the 

 yellow tint characteristic of the true D. pidex. In some lakes 

 a species was found which seemed more closely allied to D. 



