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Sentusidinium spissum
Plate 31, Figures 7, 11, 14, Plate 32, Figures 13, 14, 16, 17
Holotype: Plate 32, Figures 13, 14.
Paratype: Plate 31, Figure 14.
Type Locality: Speeton Clay Formation, early Hauterivian.
Holotype: Bed C7G, inversum ammonite Zone, slide C7G(1), E.F. O50.0, Paratype Bed C6, speetonensis ammonite Zone, slide C6(1), E.F. J28.1
Derivation of Name: From the Latin spissus, close, dense, thick- in reference to the thick-walled nature of this species.
Diagnosis: A species of intermediate size with a spheroidal body. The autophragm is thick with dense inner and spongy/microreticulate outer layers but no positive surface features. The spongy layer can thicken at cingular margins and, although no clear cingulum is discernable, it can be intermittently suggested by faint lineations. The archeopyle is apical, type (tA), normally with a detached operculum and without deep accessory archeopyle sutures between the six precingular plates. A low, conical projection can occur at the apex, formed entirely from the spongy outer autophragm layer. The ventral surfacebears a deep sulcal groove.
Dimensions: Holotype (complete): 81 × 76 μm.
Paratype (operculum detached): 71 × 86 μm.
Overall (operculum detached): 87 (81) 71 × 94 (85) 76 μm
Specimens Measured: 10
Complete specimens - 89 (85) 81 μm × 86 (81) 76 μm
Specimens Measured: 5
Remarks: This species has proved distinctive in the present study in its fairly large size and thick autophragm with a spongy/microreticulate outer layer. The spongy layer is much less dense than the inner autophragm layer and is discernable in lateral view as a thin “halo”. The spheroidal shape results in random orientation, and in polar view this clearly shows the large tetratabular apical archeopyle, which can appear significantly wider in lateral compression.
Detached opercula are easily recognised and show well the thick inner and thinner outer layers, the latter forming a low fringe (Plate 32, Figs. 16, 17). The deep sulcal groove and large apical archeopyle of Sentusidinium spissum are reminiscent of those features in Cassiculosphaeridia magna Davey 1974, although the latter is clearly distinguished by its raised reticulum. Sentusidinium spissum n. sp. ranges across the early/late Hauterivian boundary at Speeton, between Beds C7G and C6, inversum to speetonensis ammonite Zones and it has a similar range in well 14/19-21 (see text-figs. 4, 11).
Holotype: Plate 32, Figures 13, 14.
Paratype: Plate 31, Figure 14.
Type Locality: Speeton Clay Formation, early Hauterivian.
Holotype: Bed C7G, inversum ammonite Zone, slide C7G(1), E.F. O50.0, Paratype Bed C6, speetonensis ammonite Zone, slide C6(1), E.F. J28.1
Derivation of Name: From the Latin spissus, close, dense, thick- in reference to the thick-walled nature of this species.
Diagnosis: A species of intermediate size with a spheroidal body. The autophragm is thick with dense inner and spongy/microreticulate outer layers but no positive surface features. The spongy layer can thicken at cingular margins and, although no clear cingulum is discernable, it can be intermittently suggested by faint lineations. The archeopyle is apical, type (tA), normally with a detached operculum and without deep accessory archeopyle sutures between the six precingular plates. A low, conical projection can occur at the apex, formed entirely from the spongy outer autophragm layer. The ventral surfacebears a deep sulcal groove.
Dimensions: Holotype (complete): 81 × 76 μm.
Paratype (operculum detached): 71 × 86 μm.
Overall (operculum detached): 87 (81) 71 × 94 (85) 76 μm
Specimens Measured: 10
Complete specimens - 89 (85) 81 μm × 86 (81) 76 μm
Specimens Measured: 5
Remarks: This species has proved distinctive in the present study in its fairly large size and thick autophragm with a spongy/microreticulate outer layer. The spongy layer is much less dense than the inner autophragm layer and is discernable in lateral view as a thin “halo”. The spheroidal shape results in random orientation, and in polar view this clearly shows the large tetratabular apical archeopyle, which can appear significantly wider in lateral compression.
Detached opercula are easily recognised and show well the thick inner and thinner outer layers, the latter forming a low fringe (Plate 32, Figs. 16, 17). The deep sulcal groove and large apical archeopyle of Sentusidinium spissum are reminiscent of those features in Cassiculosphaeridia magna Davey 1974, although the latter is clearly distinguished by its raised reticulum. Sentusidinium spissum n. sp. ranges across the early/late Hauterivian boundary at Speeton, between Beds C7G and C6, inversum to speetonensis ammonite Zones and it has a similar range in well 14/19-21 (see text-figs. 4, 11).