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 Eist 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 fiaeone; it serves to catch and hold back the rub- 

 bish. The net or cone-dredge devised by Dr. E. A. Blrge 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. 



Dapbniidae. — By the genera, Simocepbalus, Ceriodapbnia, Scapboleheris 

 and Dapbnia. 



Macrotbricidae. — By the genera, Macrotbrix and Iliocryptus. 



Lynceidae. — By the genera, Eurjcercus, Alona, Danbevedia, Pleuroxus, 

 Cbydorus, Camptocercus and Leydigia. 



Leptodoridae. — By the genus Leptodora 



