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Hempel ('99) reports Raphidiophrys pallida Ehrbg. and Kk. elegans 
Hertwig and Less. in the plankton of Quiver Lake adjoining the 
river, and I have found an undetermined species of Acanthocystis 
and a small heliozoan resembling Nuclearta in the river plankton. 
SPOROZOA. 
Triactinomyxon sp.—In the plankton collections of each year 
there have been found free limnetic spores which unquestionably 
belong to that highly aberrant and peculiar group of organisms 
described by Stolé (’99) as Actinomyxidia and regarded by him as 
Mesozoa, but later referred by Mrazek (’00) Caullery and Mesnil 
(’04), and Leger (’04) to the Myxosporidia. The organisms de- 
scribed by Stolé were parasitic in fresh-water oligochetes, and it is 
not improbable that the limnetic spores taken in our plankton 
collections are derived from parasites in some of the numerous 
aquatic oligochetes, or other invertebrates, found along the bottom 
and shores of the stream. 
The species here referred to Triactinomyxon differs in some 
details from T. ignotum Stolé. It was found in the course of the 
six years at least once in every month of the year, but most regularly 
in May—September, and rarely and in small numbers in the colder 
months. Its transparency and long, slender, radiating, tripod-like 
arms give it a typically limnetic habit. 
Actinomyxidia, gen. et sp. indet.—Clusters of eight, or less, 
cylindrical spores radiating from a common center and bearing a 
marked resemblance in structural features to those of Triactinomyx- 
on, but lacking any anchor-like projections, were found sparingly 
in the plankton in June—September. 
The distinctively limnetic habit of these spore stages in the life- 
history of these parasites is unique among the Sporozoa, and has 
not, to my knowledge, been before noted. 
Many of the rotifers of the summer plankton, especially Brachi- 
onus and an occasional Asplanchna, have been heavily parasitized 
internally by small sac-like bodies, often pear-shaped, with the 
smaller end attached to the lorica, or of spherical or flattened form. 
They occur in such numbers at times as to be a menace to the 
rotifer population. They are usually most abundant in any given 
species at the time of, or subsequent to, its maximum occurrence. It 
