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Hystrichodinium isodiametricum

Hystrichodinium isodiametricum (Cookson and Eisenack, 1958) Stover and Evitt, 1978

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: Palaeohystrichophora isodiametrica
The shell is approximately isodiametric and divided somewhat unequally by a straight girdle with low borderes; 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 streches from just below the apex to the girdle.
Dimensions: Type 75x66 Ám, girdle 6 Ám, appendages c. 24 Ám. Paratype 70x71 Ám, girdle 5 Ám, pylome 28x20 Ám.

Affinities:
Cookson and Eisenack, 1958, p. 38: Palaeohystrichophora isodiametrica
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 apicrs and somewhat longer appendages. In P. infusorioides as preserved in the Gearle Siltstone, the shell is fusiform and the appeandages are somewhat shorter and stiffer.
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