Figs. 11-18, Plate 7, Fig. 9; Hasle, 1968c, Figs. 1, 2, and 7-9; Hasle, 1972c, p. 115; Sournia et al., 1979, Fig. 33; Hasle & Medlin, 1990b, p. 181, Plate 24.2, Figs. 11-18. Girdle view: Valve face slightly curved; valve faces of sibling cells united for the greater part of the cell length. Interstriae coarse, penetrating deeply into the cell interior, readily seen with LM. Valve view: Larger (ca. 40-70 ¿im) specimens narrowly elliptical with heteropolar apical axis, smaller specimens broadly lanceolate to broadly elliptical with isopolar apical axis. Transverse striae parallel, slightly curved near apices, two rows of large poroids, readily seen with LM. No central larger interspace (raphe uninterrupted from pole to pole, SEM). Remarks: The coarse interstriae shaped as anvils in cross section and thus similar to pseudosepta indicate a close relationship to N. seminae.
Fragilariopsis ritscheri Hustedt (Plate 67, Table 73) Synonym: Nitzschia ritscheri (Hustedt) Hasle.
References: Hustedt, 1958a, p. 164, Figs. 133, 136, and 153; Hustedt, 1958b, p. 205, Figs. 16 and 17; Hasle, 1965a, p. 20, Plate 4, Figs. 1-7, Plate 7, Fig. 8; Hasle, 1968c, Fig. 10; Hasle, 1972c, p. 115; Hasle & Medlin, 1990b, p. 181, Plate 24.2, Figs. 1-10. Valve view: Larger (ca. 40-70 /i,m) specimens narrowly elliptical, apical axis slightly heteropolar, one pole broadly rounded, the other more pointed; smaller specimens more broadly elliptical with inconsiderable heteropolarity. Valves broad in relation to their length; middle part of
F. pseudonana a
F. pseudonana valve with slightly curved margins. Transverse striae with two rows of small poroids discernible in cleaned valves mounted in a medium of a high refractive index. No central larger interspace.
Fragilariopsis atlantica Paasche (Plate 67, Table 73) Synonym: Nitzschia paaschei Hasle.
References: Paasche, 1961, p. 199, Fig. lb, Plate 1, b-f; Hasle, 1965a, p. 9, Plate 1, Figs. 1-5, Plate 2, Figs. 1-3; Hasle, 1974, p. 426; Hasle 8c Medlin, 1990b, p. 181, Plate 24.1, Figs. 1-5. Girdle view: Valves flat, cells fairly low; valves of sibling cells in ribbons united along their whole length with no interspace. Interstriae weak, discernible with LM.
Valve view: Largest (ca. 40 fim) specimens broadly linear with more or less obtuse apices, slightly heteropolar apical axis; medium-sized valves lanceolate with slightly pointed apices and isopolar apical axis; smallest specimens broadly elliptical with broadly rounded apices. Valves broad in relation to their length. Central larger interspace present; central nodule visible with LM (cleaned valves mounted in a medium of a high refractive index). Transverse interstriae more curved in smaller than in larger specimens. Stria structure not resolved with LM.
2. Apical axis isopolar; apices more or less rounded.
Fragilariopsis oceanica (Cleve) Hasle (Plate 67, Table 73) Basionym: Fragilaria oceanica Cleve.
Synonyms: Fragilaria arctica Grunow in Cleve 8c Grunow; Nitzschia grunowii Hasle.
References: Cleve, 1873b, p. 22, Plate 4, Fig. 25; Cleve 8c Grunow, 1880, p. 110, Plate 7, Fig. 124; Hustedt, 1959, p. 148, Fig. 662; Hasle, 1965a, p. 11, Plate 1, Figs. 15-19, Plate 2, Figs. 6 and 7; Hasle, 1972c, p. 115; Hasle 8c Medlin, 1990b, p. 181, Plate 24.1, Figs. 15-19. Girdle view: Cells in straight or sometimes curved ribbons; no interspace between valves of sibling cells. Pervalvar axis often high compared to that of the other Fragilariopsis spp. Mantle fairly deep, better silicified than valve face.
Valve view: Largest specimens narrowly elliptical with slightly elongated ends, medium-sized specimens more lanceolate with rounded ends, and
PLATE 67 Fragilariopsis ritscheri: valves showing size variation, striation, and heteropolarity. Fragilariopsis atlantica: valves showing size variation, slight heteropolarity, striation, and central interspace. Fragilariopsis oceanica: (a) ribbon with resting spores; (b) valves showing size variation and isopolarity. Fragilariopsis pseudonana: Valves showing size variation, striation, and isopolarity. Scale bars = 10 /¿m.
smallest specimens broadly elliptical. Interstriae on valve face weakly silicified, more strongly siliciHed on valve mantle. Raphe along the bend between valve face and mantle or slightly displaced to the mantle; central larger interspace present. Structure of striae not resolved with LM. Resting spore valves structured as vegetative valves but heavily silicified.
Fragilariopsis pseudottana (Hasle) Hasle (Plate 67, Table 73) Basionym: Nitzschia pseudonana Hasle.
Synonyms: Fragilaria nana Steemann Nielsen in Holmes, 1956, pro parte; Fragilariopsis nana (Steemann Nielsen) Paasche.
References: Holmes, 1956, p. 47, Fig. 17 pro parte; Paasche 1961, p. 201, Fig. la, Plate 1, Fig. a; Hasle, 1965a, p. 22, Plate 1, Figs. 7-14, Plate 4, Figs. 20 and 21; Hasle, 1974, p. 427; Hasle & Medlin, 1990b, p. 181, Plate 24.1, Figs 7-14; Hasle, 1993, p. 317. Valve view: Largest (ca. 15-20 /xm) specimens narrowly elliptical and smaller specimens more lanceolate with more or less rounded ends. Interstriae straight in middle part of the valves and curved closer to the apices. Fibulae and interstriae, but not striae structure resolved with LM. No central larger interspace. Remarks: Since Fragilaria nana Steemann Nielsen, basionym of Fragilariopsis nana (Steemann Nielsen) Paasche, is synonomous with Fragilariopsis cylindrus, the name Fragilariopsis nana cannot be used. No type was indicated for either Fragilariopsis pseudonana (Hasle, 1965a) or for Nitzschia pseudonana (Hasle, 1972c, p. 115); the first valid name is therefore Nitzschia pseudonana Hasle in Hasle (1974).
3. Apical axis isopolar; apices generally pointed.
Fragilariopsis rhombica (O'Meara) Hustedt (Plate 68, Table 73) Basionym: Diatoma rhombica O'Meara. Synonym: Nitzschia angulata Hasle.
References: O'Meara, 1877, p. 55, Plate 1, Fig. 2; Hustedt, 1952, p. 296, Figs. 6 and 7; Hustedt, 1958a, p. 163, Figs. 113-120; Hustedt, 1958b, p. 205, Figs. 8-11; Hasle, 1965a, p. 24, Plate 9, Figs. 1-6; Hasle, 1972c, p. 115; Hasle & Medlin, 1990b, p. 181, Plate 24.1, Fig. 6, Plate 24.2, Fig. 19, Plate 24.4, Figs. 1-6. Valve view: Largest and medium-sized specimens either lanceolate or linear with parallel margins tapering toward pointed ends and smallest specimens almost circular. Valves broad in relation to their length. Interstriae straight in the middle linear or convex part of the valve and curved in the tapering parts. Striae with two alternating rows of poroids discernible with LM. No central larger interspace.
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