. Fresh-water biology. Freshwater biology. ^36 FRESH-WATER BIOLOGY IS (14) Cells not cask-shaped, with a narrow, shallow, central constriction; end view elliptical or triangular, ends tapering or round. Spondylosium Archer. Cells 10 to 1211 broad: 8 to gii long, cells tapering towards the ends. Membrane smooth or with slight prominences. A pyrenoid in each cell-half, about which radiate from 4 to 6 chlorophyll plates The cells of the filaments are tmited by the close adher- ence of the apices of the cells. The filaments are frequently twisted and enveloped in mucus. Fig. 112. Spondylosium papi
. Fresh-water biology. Freshwater biology. ^36 FRESH-WATER BIOLOGY IS (14) Cells not cask-shaped, with a narrow, shallow, central constriction; end view elliptical or triangular, ends tapering or round. Spondylosium Archer. Cells 10 to 1211 broad: 8 to gii long, cells tapering towards the ends. Membrane smooth or with slight prominences. A pyrenoid in each cell-half, about which radiate from 4 to 6 chlorophyll plates The cells of the filaments are tmited by the close adher- ence of the apices of the cells. The filaments are frequently twisted and enveloped in mucus. Fig. 112. Spondylosium papillatum W. and G. West. (OrigiDaL) X600. 16 (13) Cells deeply constricted in the middle 17 X7 (18) Cell-halves acutely pointed or oval; upper and lower surface of each end furnished with a spine which meets a similar one on the adjoining cell; end view fusiform. . Narrow spines frequently present. In each cell-half a single axial chromatophore, composed of radiating plates about a central pyrenoid. Onychonema occurs in swamps and ponds but is not of very fre- quent occurrence in America. Fig. 113. Onyc/wnewa ioCTfi Nordstedt. X 600. (Original.) 18 (17) Cell-halves oval in outhne, with a deep central constriction; cells united into filaments by small tubercles. Sphaerozosma Archer. Cells 22 to 33/i broad and about half as long, end view elliptical; membrane smooth or with tiny warts near the ends of the cells. Sphaerozosma is distinguished from Spondylosium by the cells being united by tubercles instead of by their apices directly. 5. pulchrum var. inftatum Wolle is reported by Wolle as occur- ring in such quantities as to color the water green. Fig. 114. Sphaerozosma verlebratum "Bialis. X about 300. (After de Bary.) ng (12) End view of cells triangular or quadrangular, seldom oval. 20 (21) No space at the center between the transverse septa; cells slightly and narrowly constricted Desmidiiim Filaments long, twisted. Cells flat at the ends, i to
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