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Cassidium hexalobosum
Cassidium hexalobosum, Cookson and Eisenack, 1974
Holotype: Cookson and Eisenack, 1974, pl.26, fig.7
Age: Middle Cretaceous-Senonian
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Original description: [Cookson and Eisenack, 1974, p. 76]:
Diagnosis:
Shell flat, thin-walled, single-layered, in outline in form of a greatly rounded-off trapezoid or approximately in form of a 3/4 circle, with a circular sector separated approximately along a chord. Front-, and back-side are pressed one on top of the other in the preparation. The type exhibits an indistinct, non-decodable tabulation and at its broadest point a girdle is present which is barely visible and does not make itself conspicuous along the lateral margin. The "paratypoid" and other specimens show no tabulation. These differences are to be viewed as expression of the variability.
The surface is covered with more or less developed "shaggy" (tufted) small spines which, in the case of the type, give the impression of a coarse granulation and are of a more distinct nature solely on the left hand side of the antapex. In the "paratypoid" they show up in a more pronounced manner.
The missing (unknown) circular sector apparently represents the discarded apical portion.
The preserved shell portion displays here 6 lobes ,which are separated by deep indentations and are delineated in an indistinct parallel manner, these extend in the type specimen to the girdle and have approximately the same depth in the "paratypoid". Their upper delimitation is partially linear, partially projecting in oblique manner. Furthermore, the front-, and back-sides do not cover one another completely here.
Dimensions:
Type: 90 µm broad, about 76 µm high; paratypoid: 84 µm broad, about 74 µm high.
Remarks:
These 6 lobes are probably the best proof for a disguised more or less pronounced tabulation. They point perhaps to an apical portion consisting of 6 plates, as it occurs frequently. In unopened state, the species might be difficult to recognize.
The classification to the genus Cassidium is uncertain. The overall form (with replaced lid) is in approximate agreement; the separation-line of the apical portion does not differ in principle. For the Cassidium the occurrence of a girdle is disclaimed, however, in the case of the ?C. hexalobosum it is like not constantly present. As species-differentiating characteristic with respect to the C. fragilis (Harris), the deep indentations must be considered.
Holotype: Cookson and Eisenack, 1974, pl.26, fig.7
Age: Middle Cretaceous-Senonian
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Original description: [Cookson and Eisenack, 1974, p. 76]:
Diagnosis:
Shell flat, thin-walled, single-layered, in outline in form of a greatly rounded-off trapezoid or approximately in form of a 3/4 circle, with a circular sector separated approximately along a chord. Front-, and back-side are pressed one on top of the other in the preparation. The type exhibits an indistinct, non-decodable tabulation and at its broadest point a girdle is present which is barely visible and does not make itself conspicuous along the lateral margin. The "paratypoid" and other specimens show no tabulation. These differences are to be viewed as expression of the variability.
The surface is covered with more or less developed "shaggy" (tufted) small spines which, in the case of the type, give the impression of a coarse granulation and are of a more distinct nature solely on the left hand side of the antapex. In the "paratypoid" they show up in a more pronounced manner.
The missing (unknown) circular sector apparently represents the discarded apical portion.
The preserved shell portion displays here 6 lobes ,which are separated by deep indentations and are delineated in an indistinct parallel manner, these extend in the type specimen to the girdle and have approximately the same depth in the "paratypoid". Their upper delimitation is partially linear, partially projecting in oblique manner. Furthermore, the front-, and back-sides do not cover one another completely here.
Dimensions:
Type: 90 µm broad, about 76 µm high; paratypoid: 84 µm broad, about 74 µm high.
Remarks:
These 6 lobes are probably the best proof for a disguised more or less pronounced tabulation. They point perhaps to an apical portion consisting of 6 plates, as it occurs frequently. In unopened state, the species might be difficult to recognize.
The classification to the genus Cassidium is uncertain. The overall form (with replaced lid) is in approximate agreement; the separation-line of the apical portion does not differ in principle. For the Cassidium the occurrence of a girdle is disclaimed, however, in the case of the ?C. hexalobosum it is like not constantly present. As species-differentiating characteristic with respect to the C. fragilis (Harris), the deep indentations must be considered.