VEGA-EXPEDITIONENS VETENSKAPLIGA ARBETEN. 467 
metric, others not. There are also closely allied forms, which 
have arcuate valves and therfore belong to Rhoikoneis. The 
Rh. Bolleana 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 linear forms, 
about 10 times longer than broad, which have parallel strite, 
shortened around the central nodule. 
var. remota Grun. (A. Schm. Atl. Pl. XLVII, fig. 2) strie 4 
—53 in 0,01 mm. — Finm., Spitsb., Kara (Matotsechkin Schar). 
var. Incus Grun. (A. Schm. Atl. Pl. XLVII, fig. 7 from the 
Mediterranean Sea) Strix 4 in 0,01 mm. very slightly radiant, on 
one half of the valve interrupted. I have not seen typical 
specimens from the Arctic Sea. 
var. angusta Grun. (A. Diat. pag. 39) strie 8 in 0,01 mm. 
Greenl. (Mushroom Point), Finm., Spitsb., Kara, Cape Deschnew 
(Bast Cape).” Seems to me to be the typical N. directa W. Sm. 
var. subtilis Greg. (Pinnul.? subt. Greg. D. of CI. pag. 488, 
Pl. IX, fig. 19) strig 9—11 in 0;o1 mm. Spitsb., F: J. L., Cape 
Deschnew (East Cape), Cape Wankarema. 
var.? decussatim-striata Grun. — F. J. L. (unknown to me). 
N. transitans Cl. — Intermediate forms between N. directa 
and N. Zostereti Grun. Valves more or less abbreviate, lan- 
ceolate. Strix parallel or slightly radiant. 
forma genwina. — 6 to 4 times longer than broad, lanceolate. 
Strig coarsely lineate, 8 in 0,01 mm. almost parallel, shortened 
around the central nodule. Length 0,065 to 0,09 mm. Breadth 
0,016 mm. to 0,02 mm. — Cape Wankarema. -— P1. 36, fig. 31 
and 33. 
rar. derasa Grun. (Nav. derasa Grun: A. Diat. pag. 39; 
P1. II, fig. 46). Strie on both sides of the median line inter- 
rupted by a linear area, 8!/.—12 in 0,01 mm. in the middle, 
10—14 near the ends, not so strongly transversely lineate as 
in typical specimens, (according to Grunow the strie are 10 
in 0,01 mm. in the middle and 16 at the ends). Length 0,067 
mm. Breadth 0,015 mm. — Kara, Cape Wankarema, Cape 
Deschnew (East Cape). : 
forma minuta. — Strige 12 in 0,01 mm., distincetly trams- 
versely lineate. Length 0,035 mm. Breadth 0,012 mm. — Cape 
Deschnew (East Cape). PI. 36, fig. 37. 
form. gracilenta Grun. 1. ec. Kara. 
N. incudiformis Grun. (N. Incus abbreviata Grun. A. Diat. 
