No: 407. THE CREST OF DAPHNIA HYALINA. 88 
5 
Types. — These numerous varieties may be classed under 
five types, three of which are quite the same as those described 
for Europe under the names Pellucida, Galeata, and Gracilis, 
while the other two are peculiar to our lakes. These are the 
St. Claire form, characterized by slight elongation and tri- 
angular shape of the head, and the Gogebic form, with greatly 
elongated and compressed shell, slender antennae, and recurved 
apex of the crest. These two varieties differ most widely from 
the typical Hyalina, and at first sight appear to be entitled to 
specific rank. The most striking deviation is toward a form 
with pointed crest, the apex of which in European forms is 
ventral and in American varieties is dorsal to the median 
line of the lateral aspect. Further, the crested variety, as it 
occurs in Europe, approaches other European species, such as 
D. kahlbergiensis, while our recurved variety is very similar to 
D. retrocurva, the American representative of D. kahlbergiensts. 
Range of Variation in One Locality. — In two localities only 
did this earlier material reveal the.occurrence of more than one 
variety. In Lake Mendota two types may be distinguished, one 
closely resembling D. gracilis, the other the extreme round 
form of Lake Winnebago. Minocqua furnished forms approach- 
ing three widely differing types of development: (1) rounded 
crest, carried out into a sharp point; (2) extremely recurved 
apex; (3) triangular head with decided prominence over eye. 
Further examination, however, reveals a much wider range of 
variation for the single lake. 
In the summers of 1896, 1897, and 1898, collections were 
made from a limited region in southeastern Wisconsin, known 
as the lake district of Waukesha County, and including about 
fifty lakes varying in size from the merest pond to those four 
or five miles in length and thirty meters deep. Thirty-five 
lakes were visited in all, most of them several times, but only 
fourteen of these have, up to the present time, yielded material 
in sufficient abundance for comparative study. 
With a single exception these lakes furnish no new types, 
but in some lakes a single type with slight deviations is present, 
while others yield what might be considered distinct types, were 
it not for the occurrence of all imaginable transitions. This 
