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, -Vtr, and the basal seta of 
the triarticulate ramus is about as long as that borne on the 
next joint. In this respect this species differs from most of the 
species of the section Hi/alodaphnia. 
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 
Hyalodaphnioe , the European D. cucullcita , 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- 
<4 
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 was 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, Ill., a species which I refer to this species with 
some doubt. D. longiremis, Sars., and this species occur to- 
