Daphnia microcephala. 297 



of this margin. The variation depends rather on the form of 

 the head than on the length of the antenna. Spines are found 

 on both the dorsal and ventral edge of the valves. Two em- 

 bryos were seen in the brood cavity. 



The antennary setae are, as usual, Wt\ and the basal seta of 

 the triarticulate ramus is about as loug as that borne on the 

 next joint. In this respect this species differs from most of the 

 species of the section Hyalodaphnia. 



In all specimens collected the tip of the spine was broken off, 

 but it could not have been much longer than the figure shows 

 it. The spine is slender and resembles that of D. microcephala, 

 Sars. The anal teeth are larger than is usual in the section 

 Hyalodaphnia. This variety represents, among the American 

 Hyalodaphnice, the European D. cucullata, Sars, or D. apicata, 

 Kurz. The anal teeth are more numerous than in the European 

 forms and the caudal claws are pectinate. 



It is rather difficult to decide whether to call this form a spe- 

 cies or a variety. It is very different in shape of head from 

 any known American Hyalodaphnia and so far is undoubtedly 

 entitled to specific rank. On the other hand European experi- 

 ence shows that the forms of the section Hyalodaphnia are al- 

 most indefinitely variable in the shape of the head and that the 

 most extreme forms show connections. It has therefore seemed 

 best to call it a variety only. 



This species was found at Tomahawk lake and at Twin lake, 

 Forest county, Wisconsin. It is a pelagic form and as the two 

 localities where it occurs are about thirty miles apart, it may 

 be looked for in other lakes of this region. It w r as not found at 

 Minocqua, although Kawaquesaga lake, on which that town is 

 located, is continuous with Tomahawk lake. 



Daphnia microcephala, Sars. ( ?) . 



Plate XI, Fig. 13. 



I have found in collections from lakes Geneva and Delavan, 

 Wisconsin, in material kindly sent me by Prof. S. A. Forbes, 

 of Champaign. 111., a species which I refer to this species with 

 some doubt. D. longi?-emis, Sars.-, and this species occur to- 



