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Bands "low." Apex shallow. Otaria sometimes ending slightly below the process base and sometimes extending a short distance along the basal part of the process.

Rhizosolenia curvata Zacharias (Plate 26, Table 32) Synonym: Rhizosolenia curva Karsten.

References: Zacharias, 1905, p. 120; Karsten, 1905, p. 97, Plate 11, Fig. 2; Hasle, 1968b, p. 7, Plate 9, Fig. 8, Map 2; Sournia et al., 1979, p. 191, Fig. 20; Sundström, 1986, p. 20, Figs. 57-63; Priddle et al., 1990, p. 118, Plate 15.2, Fig. 3.

Cells curved. Otaria comparatively small, ending below valve apex.

Rhizosolenia acicularis Sundström (Plate 26, Table 32) Reference: Sundström 1986, p. 22, Figs. 6 and 64-69. Otaria pointed, narrow, ending below process base. Perhaps closely related to R. styliformis but differs in shape and position of otaria and in distribution.

Rhizosolenia borealis Sundström (Plate 27, Table 32) Synonym: Rhizosolenia styliformis var. oceanica Wimpenny pro parte. References: Wimpenny, 1946, p. 279, Text Fig. Id; Hasle, 1975, p. 104, Figs. 8-20; Sundström, 1986, p. 30, Figs. 10, 11, and 80-87. Otaria extending to about half the length of the thicker basal part of the process.

Remarks: The reasons for regarding R. borealis and R. polydactyla as two distinct species are the difference in the distribution and the fact that R. polydactyla is dimorphic and R. borealis is not (Sundström, 1986, p. 32).

Distribution:

R. borealis—northern cold water region. R. styliformis—northern part of North Atlantic Ocean. R. acicularis and R. formosa—warm water region. R. curvata—Subantarctic/Antarctic convergence.

2. Two dorsiventral columns of segments: dimorphism.

Rhizosolenia antennata (Ehrenberg) Brown f. antennata (Plate 27, Table 33) Basionym: Dicladia antennata Ehrenberg.

Synonyms: Rhizosolenia bidens Karsten pro parte; Rhizosolenia hebetata f. bidens Heiden in Heiden 8c Kolbe.

References: Ehrenberg, 1844b, p. 201; Karsten, 1905, p. 98, Plate 9, Fig. 13; Van Heurck, 1909, Plate 4, Fig. 64; Brown, 1920, p. 233, Fig. 8; Heiden 8c Kolbe, 1928, p. 519, Figs. 158-161; Sundström, 1986, p. 42, Figs. 115,119, and 120; Priddle et al., 1990, p. 117, Plate 15.1, Figs. 5a-5c. Two processes, no otaria.

R. hebetata f. hebetata

R. polydactyla

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