Key To Species

la. Valve areolae distinct, central annulus mostly indistinct 2

lb. Valve areolae indistinct, striae wavy, annulus distinct 3

2a. Radial and spiraling striae, external part of labiate process short

P. pseudodenticulata3 (Hustedt) Jouse

2b. Areolation fasciculate, external part of labiate process long

P. denticulata Simonsen

3 a. Labiate process close to the valve margin with two small strutted processes on a radial line on each side P. pentaportula Syvertsen 8c Lange

3b. Labiate process at some distance from the valve margin, no regular arrangement of strutted processes close to the labiate process

P. glacialis (Grunow) Jorgensen

3 Basionym: Coscinodiscus pseudodenticulatus Hustedt.

Porosira glacialis

Porosira pseudodenticulata a Wc Skeletonema a Wc Skeletonema

S. costatum

S. menzellii

Porosira pentaportula

PLATE 3 Porosira glacialis and P. pseudodenticulata: (a) single cell in girdle view; (b) P. glacialis valve with central annulus, processes, and sector with wavy areolation; (c) P. pseudodenticulata with straight rows of areolae and no annulus. Porosira pentaportula: (a) single cell in girdle view; (b) valve with process pattern; (c) detail, labiate process with two strutted processes on each side.

Species

Pervalvar axis (|xm)

Diameter (jim)

Areolae in 10 urn

P. denticulata P. glacialis P. pentaportula P. pseudodenticulata

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