PLATE 21 Azpeitia nodulifera: (a) girdle view, steep mantle; (b) valve with areolation. Scale bar = 10 p,m.
slits leading into the processes, A. tabularis by the hyaline ring close to the margin, A. neocrenulata by the depressions on the valve mantle, and A. nodulifera by the large labiate process close to valve center. Azpeitia barronii, which also has a large central labiate process, is distinguished from A. nodulifera by its sublinear pattern of equally sized areolae over most of the valve.
Genus Hemidiscus Wallich 1860 (Plate 22, Table 28) Type: Hemidiscus cuneiformis Wallich.
References: Wallich, 1860, p. 42, Plate 2, Figs. 3 and 4; Hustedt, 1930, p. 904, Fig. 542; Cupp, 1943, p. 170, Fig. 121; Hendey, 1964, p. 94, Plate 22, Fig. 9; Simonsen, 1972, 1975; Fryxell et al. 1986b, p. 25, Fig. 26.
The genus encompasses two species, the type, and Hemidiscus kanayanus Simonsen (Simonsen 1972).
Areolation radial, partly in bundles.
Marginal ring of labiate processes with a pseudonodulus midway on the straight margin.
Characters showing differences between species: Size of areolae.
Fasciculation distinct in H. cuneiformis, indistinct in H. kanayanus. Annulus distinct in H. kanayanus.
H. kanayanus—warm water region (described from the Indian Ocean, recorded also from the equatorial Pacific).
H. cuneiformis—warm water region (may be transported far north along the Norwegian coast; Hustedt, 1930). How to identify: The subcircular valve outline is shared with Palmeria and may cause confusion if the material is examined as whole cells in water mounts. The distinctive feature of Hemidiscus, the pseudonodulus, is readily
PLATE 22 Hemidiscus cuneiformis: (a) cell in girdle view; (b) valve. Scale bar = 50 um. Roperia tesselata: (a) cell in girdle view; (b) valve with areolation and pseudonodulus. Scale bar = 10 jum. Pseudoguinardia recta: chain in girdle view. After von Stosch (1986). Scale bar = 50 /xm. Actinoptychus senarius: (a) girdle view with undulated valve; (b) valve with sectors. Scale bar = 10 /xm.
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