Welcome to the Diatom Image Database! The Periphyton Group at Florida International University created and maintains the Diatom Image Database, which includes over 980 diatom taxa found in the greater Everglades region of south Florida. Please send questions or comments about the Diatom Image Database to Franco Tobias .
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(W. Smith) Griff. & Henfr.
Patrick, R. & Reimer, C. W (1966). The Diatoms of the United States I. Monographs of the Academy of Natural Sciences of Philadelphia. Pennsylvania. pp. 323; 346-347 (pl.24:7)
Pleurosigma obscurum W. Sm. 1852; Gyrosigma obscurum (W. Sm.) Griff. & Henfr. 1856
Valve is slightly sigmoid but is linear for more than half the valve length, then attenuating to rather narrowly rounded ends; valve surface is strongly arched with a rather elevated, eccentric axial portion; raphe is also eccentric throughout and sigmoid, close to the margins near the ends; proximal raphe ends are indistinct, but appear straight; central area is quite small, orbicular or longitudinally elliptical; terminal area inconspicuous; transverse striae (essentially perpendicular to the axial area, but appearing undulate due to the valve contour) are much more conspicuous than very fine longitudinal striae (which are essentially parallel to the axial area, but are unresolved except with good optics); combination of valve undulation and valve curvature gives appearance of oblique striae; length is 85-150µm, breadth is 10-15µm; striae count is 26-30 in 10µm (transverse striae) and about 40 in 10µm (longitudinal striae)