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Palaeohystrichophora isodiametrica

Palaeohystrichophora isodiametrica Cookson and Eisenack, 1958

Now Hystrichodinium. Originally Palaeohystrichophora, subsequently (and now) Hystrichodinium.
Holotype: Cookson and Eisenack, 1958, pl. 12, figs.11-12
Locus typicus: Carnavron Basin, W Australia
Stratum typicum: Campanian - Early Maastrichtian

Original description: Cookson and Eisenack, 1958, p. 38
The shell is approximately isodiametric and divided somewhat unequally by a straight girdle with low borders; both the epitheca and hypotheca are broadly dome-shaped to flat. The outer membrane, which is thin and transparent and lies close to the internal capsule, especially at the apex and antapex, is covered with numerous long wavy appendages. The example shown in pl.12, fig.11 has a large trapezoid shaped pylome which stretches from just below the apex to the girdle.

Dimensions: Type - 75 x 66 µm, girdle 6 µm, appendages c. 24 µm. Paratype - 70 x 71 µm, girdle 5 µm, pylome 28 x 20 µm.

Affinities:
Cookson and Eisenack, 1958, p. 38: In the type of ornamentation, Palaeohystrichophora isodiametrica resembles P. infusorioides Defl., but differs from this species in being approximately as along as broad and in having broadly rounded apices and somewhat longer appendages. In P. infusorioides as preserved in the Gearle Siltstone, the shell is fusiform and the appendages are somewhat shorter and stiffer.
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