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Note. +, Present; absent; ?, data uncertain. " One ring at the junction of valve face and mantle.

b The second ring including the two macrolabiate processes 2-3 areolae from margin.

Note. +, Present; absent; ?, data uncertain. " One ring at the junction of valve face and mantle.

b The second ring including the two macrolabiate processes 2-3 areolae from margin.

Coscinodicus asteromphalus Ehrenberg (Plate 15, Tables 20a and 20b)

References: Ehrenberg, 1844a, p. 77; Ehrenberg, 1854, Plate 18, Fig. 45; Hustedt, 1930, p. 452, Figs. 250 and 251; Hasle 8c Lange, 1992, p. 42, Figs. 1-14.

Girdle view: Cells discoid with slightly convex valves; valve center depressed and valve mantle gently sloping. Numerous large rounded plate-like chloroplasts.

Valve view: Central rosette of somewhat larger areolae present, usually not prominent. Decussating arcs fairly distinct. No hyaline lines. Cribra just visible with LM. Ring of processes close to valve margin visible with LM. Interstitial meshes (probably smaller areolae) present at the points of origin of short incomplete striae. Larger labiate processes about 120-135° apart, comparatively small.

Distinctive features: Compared to C. argus and C. centralis, which are the most similar species, C. asteromphalus has the ring of processes closer to the margin.

Coscinodiscus centralis Ehrenberg (Figs. 6a-6c, Plate IS, Tables 20a and 20b)

References: Ehrenberg, 1844a, p. 78; Ehrenberg, 1854, Plate 18, Fig. 39, Plate 21, Fig. 3, Plate 22, Fig. 1; Hustedt, 1930, p. 444, Fig. 243; Semina 8c Sergeeva, 1980; Hasle 8c Lange, 1992, p. 45, Figs. 15-30. Girdle view: Cells discoid; valves gently convex. Numerous small platelike chloroplasts.

Valve view: Distinct rosette of large areolae (Fig. 6b), sometimes with a small hyaline area in the middle. Areola rows grouped into narrow bundles bordered by hyaline lines, distinct in weakly silicified valves and indistinct in coarsely silicified valves. Decussating arcs in the central part of the valve. Hyaline lines associated with labiate processes at the valve margin. Interstitial meshes present, identical with the pentagonal areola at the point of origin of an incomplete stria or an adjacent larger areola. Cribra resolved with LM (Fig. 6b), consisting of one central pore and a marginal ring of pores. Marginal processes readily resolved with LM; the smaller processes are long necked and slightly curved, the two larger processes, ca. 135° apart, have two "horns" (Fig. 6c). Distinctive features: Distinguished from C. argus and C. asteromphalus by the central areolae distinctly set off from the much smaller surrounding areolae, and the cribra and processes readily resolved with LM; and distinguished from C. concinnus by the shorter pervalvar axis, the more coarsely structured valves, and the marginal processes closer to the valve margin (Plates 15 and 16).

Coscinodiscus concinnus Wm. Smith (Plate 16, Tables 20a and 20b) References: Smith, 1856, p. 85; Hustedt, 1930, p. 442, Figs. 241 and 242; Boalch, 1971, Plate 2; Brooks, 1975; Hasle 8c Lange, 1992, p. 50, Figs. 31-48.

Girdle view: Cells thin walled; valves convex. Numerous small chloroplasts, fimbriate in outline, markedly H shaped when dividing. Marginal processes discernible in water mounts. Valve view: Central rosette large with a star-shaped hyaline area in the middle. The size of the hyaline area and the development of areola walls variable. Areola rows in bundles bordered by distinct hyaline lines running from marginal labiate processes toward valve center (Plate 16). Interstitial meshes, sometimes visible, probably identical with the pentagonal areola at the point of origin of each incomplete stria. The cribra barely seen with LM. Two larger marginal processes, ca. 135° apart, with raised parts as well as the smaller marginal processes, readily seen with LM.

Distinctive features: Greater distance between valve margin and processes than in C. centralis, C. concinniformis, and C. ivailesii; species with which C. concinnus may be confused.

Coscinodiscus wailesii Gran & Angst (Plate 16, Tables 20a and 20b) References: Gran 8c Angst, 1931, p. 448, Fig. 26; Schmid 8c Volcani, 1983; Takano, 1990, pp. 250-251; Schmid, 1990; Hasle 8c Lange, 1992, p. 55, Figs. 49-62.

Girdle view: Cells low to tall cylindrical, often as high as wide, and rectangular in outline at a certain focus. Valves flattened with a concentric depression near the steep high mantle. Numerous chloroplasts irregular in outline. Marginal processes discernible in water mounts. Valve view: Prominent central hyaline (unperforated) area; wide interstriae (hyaline lines) radiating from the central area. Irregular fasciculation formed, partly by wider interstriae, partly by distinct incomplete striae, originating near the valve center at a labiate process or a small hyaline area (area of solid silica). Cribra visible with LM. One ring of smaller processes in the junction zone between valve face and mantle, and one ring including two larger processes, 120-180° apart, close to the valve margin. Processes in the first ring more densely spaced than those in the second ring. Hyaline lines more conspicuous and regular on valve mantle than on valve face, associated with processes. Distinctive features: High, steep mantle with hyaline lines and two marginal rings of processes.

Coscinodiscus concinniformis Simonsen (Plate 17, Tables 20a and 20b) References: Simonsen, 1974, p. 14, Plates 10 and 11; von Stosch, 1986, p. 303, Figs. 5 and 6. Girdle view: Cells cylindrical, as high as wide or higher. Girdle consisting of several columns of segments, curved with the two valves inclined toward each other. Valves uniformly and moderately convex; mantle extremely low. Weakly silicified. Numerous small chloroplasts. Valve view: Prominent central hyaline (unperforated) area from which wide interstriae (hyaline lines) bordering bundles of radial areola rows radiate and partly branch. Labiate processes at the points of origin of incomplete striae. One ring of processes close to the valve margin, each process at the end of a hyaline line. Processes discernible with LM. The two larger processes ca. 125° apart.

Distinctive features: Distinguished in valve view from C. wailesii by one ring of processes on valve face and from C. concinnus by scattered processes on valve face and the ring of processes closer to valve margin.

Coscinodiscus alboranii Pavillard (Plate 15, Tables 20a and 20b) References: Pavillard, 1925, p. 13, Fig. 16; von Stosch, 1986, pp. 295-303. Girdle view: Cells cylindrical, up to 1.5 times as long as wide. Valves convex, flattened in the center, and nearly semiglobular in small cells. Four lobed or oval chloroplasts. Cell wall extremely weakly silicified.

Valve view: (structures seen in air mounts with phase contrast) A circular central area without areolae, distinct hyaline lines between the central area and one marginal ring of processes. Two larger processes, ca. 125° apart, closer to the margin than the smaller processes. Valve face with two types of areolae, the rarer of which appears darker in phase contrast. Valve margin usually with a special type of areolae, endochiastic areolae, appearing as dark circlets with an internal structure similar to a cross. Distinctive features: Two types of valve face areolae; endochiastic areolae on valve mantle.

Coscinodiscus jonesianus (Greville) Ostenfeld (Plate 17, Tables 20a and 20b)

Basionym: Eupodiscus jonesianus Greville.

References: Greville, 1862, p. 22, Plate 2, Fig. 3; Ostenfeld, 1915, p. 13, Fig. 7; Hustedt, 1930, p. 438, Fig. 239; Hendey, 1964, p. 79; Makarova, 1985, p. 52, Plate 2; Takano, 1990, pp. 246-247. Girdle view: Cells about as high as wide. Valves convex, slightly concave in the center.

Valve view: Central rosette of larger areolae more or less distinct. Areolae in radial and spiraling rows. Cribra visible with LM. At about half radius an irregular ring of interstitial meshes (probably labiate processes). One marginal ring of processes, visible with LM, with hyaline lines bordered by one row of slightly larger areolae on either side toward the valve center. Inside the marginal ring two larger processes with prominent external areolated protuberances, ca. 100° apart. Distinctive features: Large external protuberances of the two larger marginal processes.

Coscinodicus marginatus Ehrenberg (Plate 18, Tables 20a and 20b) References: Ehrenberg, 1844a, p. 78; Ehrenberg, 1854, Plate 18, Fig. 44, Plate 33/12, Fig. 13, Plate 38b/22, Fig. 8; Hustedt, 1930, p. 416, Fig. 223; Hendey, 1964, p. 78, Plate 22, Fig. 2; Sancetta, 1987, p. 231, Plate 1, Figs. 1-13.

Girdle view: Cells discoid, thick walled. Valves flat or nearly so with steeply sloping or straight mantle. Several small rounded chloroplasts. Valve view: No central rosette. Coarse areolae in irregular radial rows. Cribra discernible with LM, processes not. Distinctive feature: The coarse areolation.

B. Frustules coin shaped.

Coscinodiscus radiatus Ehrenberg (Figs. 6d and 6e, Plate 18, Tables 20a and 20b)

References: Ehrenberg, 1841a, p. 148, Plate 3, Fig. 1; Hustedt, 1930, p. 420, Fig. 225; Hendey, 1964, p. 76, Plate 22, Fig. 7; Hasle & Sims, 1986a,

Coscinodiscus

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