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metric, otliers not. There are also closely allied forms, which
liave arcuate valves and therfore belong to Rhoikoneis. The
Rh. Ii olleana Grun. is really nearly allied to the group of Nav.
directa. Although all the forms of this section in my opinon
are nearly allied, it may be necessery to name them and
arrange them.
To N. directa I refer all slender, or almost liriear forms,
about 10 times longer than broad, which have parallel striae,
shortened around the central nodule.
var. remota Grun. (A. Schm. Atl. Pl. XLVII, fig. 2) striae 4
—5 in 0,oi mm. — Finm., Spitsb., Kara (Matotschkin Schar).
var. Incus Grun. (A. Schm. Atl. Pl. XLVII, fig. 7 from the
Mediterranean Sea) Striae 4 in 0,oi mm. verv slightly radiant, on
one half of the valve interrupted. I have not seen typical
specimens from the Aretie Sea.
var. angusta Grun. (A. Diat. pag. 39) striae 8 in 0,oi mm.
Greenl. (Mushroom Point), Finm., Spitsb., Kara, Cape Deschnew
(East Cape). Seems to me to be tlie typical N. directa W. Sm.
var. subtilis Greg. (Pinnul.? subt. Greg. D. of Cl. pag. 488.
Deschnew (East Cape), Cape Wankarema.
var.? decussatim-sfriafa Grun. — F. J. L. (unknown to me).
N. transit ans Cl. — Intermediate forms between N. directa
and N. Zostereti Grun. Valves more or less abbreviate,
lan-ceolate. Strise parallel or slightly radiant.
forma genuina. — 6 to 4 times longer than broad, lanceolate.
Striae coarsely lineate, 8 in 0,oi mm. almost parallel, shortened
around the central nodule. Length 0,o65 to 0,09 mm. Breadth
0,oig mm. to 0,02 mm. — Cape Wankarema. — Pl. 36, fig. 31
and 33.
var. derasa Grun. (Nav. derasa Grun. A. Diat. pag. 39,
Pl. II, fig. 46). Striae on both sides of the median line
interrupted by a linear area, 8 1 •>—12 in 0,oi mm. in the middle,
10—14 near the ends, not so strongly transversely lineate as
in typical specimens, (according to Grunow the striae are 10
in 0,oi mm. in the middle and 16 at the ends). Length 0,06?
mm. Breadth 0,oi5 mm. — Kara, Cape Wankarema, Cape
Deschnew (East Cape).
forma minuta. — Striae 12 in 0,oi mm., distinctly
transversely lineate. Length 0,o35 mm. Breadth 0,012 mm. — Cape
Deschnew (East Cape). Pl. 36, fig. 37.
form. gracilenta Grun. 1. c. Kara.
N. incudiformis Grun. (N. Incus abbreviata Grun. A. Diat.
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