Key To Genera

la. Marginal ridge present 2

lb. Marginal ridge absent, intercellular spaces missing 3

2a. Cells in inseparable or separable ribbons, seldom solitary 4

2b. Cells solitary 5

3a. Cells rectangular in broad girdle view Helicotbeca, p. 234

3b. Cells like a parallelogram in broad girdle view. Neostreptotheca, p. 235 4a. Ribbons with conspicuous intercellular spaces Bellerochea, p. 227 4b. Cells in ribbons joined by a slight overlap of a conspicuous marginal ridge

Lithodesmium, p. 232

5a. Marginal ridge conspicuous, often fringed, no defined elevations at valve corners Ditylum, p. 230

5b. Marginal ridge inconspicuous, well defined elevations at valve corners. . Lithodesmioides, p. 231

Genus Bellerochea Van Heurck 1885 emend, von Stosch 1977 (Plate 48, Table 57)

Type: Bellerochea malleus (Brightwell) Van Heurck. Basionym: Triceratium malleus Brightwell.

References: Brightwell, 1858b, p. 155, Plate 8, Figs. 6 and 7; Van Heurck, 1880-1885, p. 203, Plate 114, Fig. 1; Hustedt, 1930, p. 781, Fig. 456; Hendey, 1964, p. 122, Plate 6, Fig. 5; Drebes, 1974, p. 95, Figs. 80a and 80b; Hasle, 1975, Figs. 152-154; von Stosch, 1977, p. 128, Text Fig. 1, Figs. 1-70; von Stosch, 1987, p. 74, Figs. 204-208; Takano, 1990, pp. 294-295.

Generic characters: Cells in ribbons. Cells very weakly silicified. Cells in broad girdle view roughly rectangular. Cells in valve view biangular to quadrangular, rarely three or four armed.

Short elevation at each corner of the valve; those of adjacent cells in ribbons abutting.

Valves consisting of tracery of siliceous costae covering valve mantle, marginal ridge and most of valve face. Bilabiate process with long external tube. Chloroplasts numerous, oval and slightly constricted.

Characters showing differences between species: Type of ribbons (separable or inseparable). Shape of intercellular spaces. Location of bilabiate process.

Sellerochea horologicales Bellerochea malleus

Helicotheca tamesis

Ditylum brightwellii

Lithodesmium undulatum Neostreptotheca subindica

PLATE 48 Bellerochea horologicalis: chain, short valve elevations and intercellular spaces. Bellerochea malleus: (a) short chain; (b and c) two types of valves. Ditylum brightwellii: (a) single cell with outer parts of bilabiate process; (b) cell with resting spore; (c) valve view. Helicotheca tamesis: twisted chain. Lithodesmium undulatum: (a) short chain; (b) valve with central bilabiate process and depressions across the corners. Neostreptotheca subindica: chain in girdle view. Scale bars = 20 /¿m.

Pervalvar axis Apical axis Transapical axis Mantle costae Species (p-m) (p.m) (pm) in 10 p.m

B. horologicalis

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