IOWA ACADEMY OP SCIENCES. 
171 
offer good collecting ground at that season of the year, as they 
were nearly all dry. As we did not wish to overburden our- 
selves, we did not collect dried mud from the ponds and water 
courses. 
Collections were made in a few places from the streams, but 
principally from West and East Okoboji and Spirit Lake, rang- 
ing from the surface to a depth of twenty feet. With the 
limited apparatus and short time at our disposal, not all the 
species of the lake were taken, very probably only a minority. 
To make a thorough investigation the apparatus should be such 
that hauls could be made among the weeds and along the bot- 
tom of the lake, as well as in the clear surface water. Not only 
should the nets be such as are needed to collect from places of 
all kinds, but such should be used as are necessary to deter- 
mine the quantity of life in the water. For collecting in open 
water or where there is some rubbish, the ordinary fine-meshed 
net protected by two coarser nets, one outside and the other 
inside may be used. The inner coarse net should not be as 
deep as the fine one; it serves to catch and hold back the rub- 
bish. The net or cone-dredge devised by Dr. E. A. Birge of 
Wisconsin,. is the best for collecting among weeds. For quanti- 
tative work the plankton apparatus should be used. This is so 
arranged that the net can be drawn through the water at a 
definite rate of speed, the speed being regulated so there will 
be no overflow of water from the mouth of the net. The con- 
tents of the net are determined quantitatively as compared 
with the known amount of water that passed through. 
As yet I have determined no species outside the order Clad- 
ocera. Of this order probably twenty-five species and varieties 
have been noted but no new ones have been described, nor have 
any new to America been found. Undoubtedly, with better 
apparatus and with more literature upon the subject, many 
more species may be collected and determined. 
The following families are represented in the collections: 
Sididae . — By the genera, Sida and DapbneJla. 
Daphniidae . — By the genera, Simocepbalus, Ceriodaphnia, Scapholeberis 
and Daphnia, 
Macrothricidae . — By the genera, Macrothrix and lliocryptus. 
Ljnceidae . — By the genera, Eurycercus, Alona, Dunhevedia, PleuroxuSy 
Chydoras, Camptocercus and Leydigla. 
Leptodoridae . — By the genus Leptodora 
