272 
IOWA ACADEMY OF SCIENCE Vor.. XXVII, 1920 
Collections were made at Okoboji from the several localities 
studied, bolting-silk tow-nets with 29,929 meshes to the square 
inch being used. A Birge bucket was also used to some extent; 
the bolting-silk in this was the same gauge as that of the tow-nets. 
Most of the material was studied in a fresh condition. No really 
satisfactory method of preserving the il-loricate forms was found ; 
the best that could be done was to narcotize them with a solution 
of nicotine and then to gradually add alcohol until a strength of 
from fifty to sixty per cent was reached. This method had the 
disadvantage of shrinking many of the il-loricates, even though 
the alcohol was added very slowly. By far the most satisfactory 
studies were those made from living specimens. 
This report consists of an itemized statement as to the occur- 
rence and abundance of the several species. The revised termin- 
ology as brought out by Harring ® is used throughout. A thumb- 
nail sketch of each species recorded is to be found in the two 
plates (Plates VI and VII). These drawings were made, for 
the most part, from life; in many of the loricates, the sketch is 
merely the outline of the lorica. The sketches are included to 
give to those unfamiliar with the terminology a definite idea as 
to the wide variety of forms found in this rather limited region. 
The numbered localities on the map (Fig. 49) indicate the 
principal collecting grounds. Following is a brief description of 
each of these ; the numbers correspond with those on the map. 
1. Lake Okoboji. Collections made in Lake Okoboji were 
confined to surface tows and tows at a depth of about five feet, 
usually not more than a few rods from the shore. Ceratophyllum, 
Myriophyllum, Potamogeton, V allisneria, and numerous species 
of algae are found near the shore, and rotifers occur in consider- 
able numbers among these plants. 
2. Drainage canal. The drainage canal is the collecting ground 
par excellence for rotifers. It is almost a mile long, from ten to 
fifteen feet wide, and about ten feet deep, filled almost to the 
surface of the water with aquatic plants. The entrances from 
the lake are choked with sand; there is no current except such 
sluggish water movements as may be set up by the wind. 
3. Sand-bar pond. This is a shallow pond with two openings 
from the main lake, situated on a sand-bar at the mouth of Miller’s 
bay. Its shores are bordered by marsh grasses, sedges, and 
reeds; duckweed also is found here in great abundance. The 
depth of the pond is nowhere more than two or three feet. 
5 Idem. 
