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IOWA ACADEMY OF SCIENCE Voi,. XXVII, 1920 
in tows made on two consecutive days only, near the middle of August. 
Several specimens were found on each of the two days. 
Filinia cornuta (Weisse) (Plate VII, Fig. 17). A few individuals 
were found near the entrance of the canal (2). 
Filinia longiseta (Ehrenberg) (Plate VII, Fig. 18). This species was 
abundant in Lake Okoboji (1), the canal (2), the sand-bar pond (3), 
and Gull Point kettle hole (11) ; a few individuals were found in kettle 
hole (6), in a creek near Egralharve (9), in the fish ponds (16), and in 
Little Sioux river (21). 
Filinia passa (Muller) (Plate VII, Fig. 19). Not quite so abundant as 
F. longiseta; found in Lake Okoboji (1), in kettle hole (5), and in a kettle 
hole near West Okoboji (10). 
ORDER FLOSCULARIACBA 
Floscularia ringens (Linnaeus) (Plate VII, Fig. 20). Found on 
Ceratophyllnmy Myriophyllum, and others of the larger aquatic plants, 
but never on fresh, green, young plants. Collected from Miller’s bay, 
Lake Okoboji (1), and from the sand-bar pond (3). 
Limnias ceratophylli Schrank (Plate VII, Fig. 21). Found on Cerato- 
phyllum, often with Floscularia. Collected from Miller’s bay. Lake Oko- 
boji (1), and from the sand-bar pond (3). 
Ptygura longicornis (Davis) (Plate VII, Fig. 22). Found in great 
abundance among floccose material on old Ceratophyllum; not collected 
here on any other water plant. Sand-bar pond (3). 
Sinantherina socialis (Linnaeus) (Plate VII, Fig. 23). Clusters are 
found on the tips of Ceratophyllum leaf-lobes, like globular balls of gray 
jelly. Fairly rare here. Sand-bar pond (3). 
Lacihularia flosculosa (Muller) (Plate VII, Fig. 24). Collected from 
Lake Okoboji (1), the canal (2), and the sand-bar pond (3). This 
species was found in great abundance on the tips of the leaf-lobes of 
Ceratophyllum, being the most common of all attached rotifers in this 
region. It seems to be profusely distributed in the lake. Of sixty-eight 
colonies of social rotifers examined from one collection, sixty-seven 
were of this species, and one was Sinantherina socialis. The color of the 
colony is brownish yellow to salmon; the species is easily recognized by 
the color and by the four opaque warts or collar knobs. The collar 
knobs of the specimens from the sand-bar pond (3) and from the canal 
(2) are almost black; those of specimens found on Ceratophyllum in the 
open lake (1) are light brown. Colonies were found also on the roots of 
the common duckweed and of Lemna trisulca. 
Conochilus hippocrepis (Schrank) (Plate VII, Fig. 25). Found in great 
numbers in kettle hole (6) on one day only, July 7, a sunny, cool day. 
Conochiloides dossuaris (Hudson) Plate VII, Fig. 26). This species 
was first found in kettle hole (4) ; later it was found rarely in the canal 
(2), Marble lake (20) and one specimen from Lake Okoboji (1). 
ORDER COLLOmECACEA 
Collotheca algicola (Hudson) (Plate VH, Fig. 27). Found in colonies 
of Rivularia pisum, the animal being embedded in the gelatine of the 
