This plant is so definitely restricted to soft water habitats that it 

 may be used as an index organism for acid conditions in which the 

 pH is 6.0-6.8. It is a common component of a flora in which desmids 

 predominate, and there is some evidence that high organic acid 

 content of the water results in huge Eremosphaera cells. 



Common in many acid lakes and Sphagnum bog ponds. Mich., 

 Wis. 



EXCENTROSPHAERA Moore 1901, p. 322 



Cells spherical or ellipsoid, free-floating, intermingled with other 

 algae, the wall thick and often lamellate; chloroplasts numerous 

 cone-shaped bodies arranged at the periphery and directed inward, 

 each with many small pyrenoids; reproduction by aplanospores. 



Excentrosphaera viridis Moore 1901, p. 322 

 PI. 46, Figs. 15, 16 

 Characteristics as described for the genus; cells 22-55/^ in diam- 

 eter; spores (not observed in our collections) 2-3/j. in diameter. 



Tychoplankter; in shallow water of lake margins and soft water 

 or acid swamps. Mich. 



ECHINOSPHAERELLA G. M. Smith 1920, p. 128 



Free-floating, globose cells, entirely covered with long, stout, 

 tapering spines; chloroplast 1, cup-shaped and parietal, containing 

 a single pyrenoid. The genus is monotypic. 



Echinosphaerella limnetica G. M. Smith 1920, p. 128 

 PI. 51, Figs. 1, 2 



Characteristics as described for the genus; cells 9-12/x in diameter 

 exclusive of spines; spines 2.5-3/a wide at the base, 20-25/a long. 



This species should be compared with desmid zygospores, many 

 of which have spiny walls and greatly resemble Echinosphaerella. 

 Differentiation can be made on the basis of the chloroplast, there 

 being no definitely shaped chlorophyll-bearing body in the desmid 

 zygospore, but a dense, rather shapeless mass. 



Rare, in plankton. Wis. 



TREUBARIA Bernard 1908, p. 169 



Free-floating, pyramidal or flattened 3- to 4-angled unicells, the 

 angles rounded or produced to form a stout, thick-based spine 

 which is either tapering or has subparallel sides; the margins of 

 the cell concave between the angles; chloroplasts 1-4, parietal, 



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