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Tenua cirrita
Plate 28, Figures 3, 4, 7
Holotype: Plate 28, Figure 3
Paratype: Plate 28, Figure 7
Type Locality: Speeton Clay Formation, Division C7, early Hauterivian, inversum ammonite Zone. Holotype: Slide C7F(1), E.F. G31.0, Paratype Slide C7B(4), E.F. O47.0
Derivation of Name: From the Latin cirritus, having fine filaments– in reference to the surface ornament.
Diagnosis: Cyst composed of autophragm only, sub-circular with two closely-spaced, asymmetrically-sited antapical protuberances, the left better-developed and approximally centrally placed. Very fine surface ornament is in the form of short, slender, flat-ended spines which occasionally link at some point along their length. Complete spine cover is the norm. Ornament is significantly reduced or absent from a transverse sulcal feature running across the cyst from a shallow sulcal notch to the ventral antapex. An increase in spine height is seen over each antapical protrusion. Partial penitabular alignment of ornament can outline tabulation and some loss of mesotabular ornament can also occur, particularly on the dorsal surface. Archeopyle type tA, principal archeopyle suture zigzag with sulcal notch offset to the left.
Dimensions: Holotype (operculum detached): 71 × 84 μm.
Paratype (operculum detached): 71 × 78 μm.
Overall (operculum detached) - 78 (67) 56 μm × 94 (77) 63 μm
Specimens Measured: 29
Remarks: The main characteristic features of this species are its very fine, dense spines and the close spacing of its antapical protrusions. The spines are delicate and can occasionally be linked laterally by cross-bars, although never forming a complete distal reticulum as in Canningia.
Tabulation may be partially marked by penitabular alignment of spines, and this can be enhanced by some mesotabular reduction or loss of ornament so that some pandasutural areas can be clearly seen, particularly on the dorsal surface. This is an uncommon feature, however.
This species is a valuable marker for the latter part of the early Hauterivian; it was recorded between Speeton Beds C9A and C7B, upper regale to inversum ammonite Zones.
Holotype: Plate 28, Figure 3
Paratype: Plate 28, Figure 7
Type Locality: Speeton Clay Formation, Division C7, early Hauterivian, inversum ammonite Zone. Holotype: Slide C7F(1), E.F. G31.0, Paratype Slide C7B(4), E.F. O47.0
Derivation of Name: From the Latin cirritus, having fine filaments– in reference to the surface ornament.
Diagnosis: Cyst composed of autophragm only, sub-circular with two closely-spaced, asymmetrically-sited antapical protuberances, the left better-developed and approximally centrally placed. Very fine surface ornament is in the form of short, slender, flat-ended spines which occasionally link at some point along their length. Complete spine cover is the norm. Ornament is significantly reduced or absent from a transverse sulcal feature running across the cyst from a shallow sulcal notch to the ventral antapex. An increase in spine height is seen over each antapical protrusion. Partial penitabular alignment of ornament can outline tabulation and some loss of mesotabular ornament can also occur, particularly on the dorsal surface. Archeopyle type tA, principal archeopyle suture zigzag with sulcal notch offset to the left.
Dimensions: Holotype (operculum detached): 71 × 84 μm.
Paratype (operculum detached): 71 × 78 μm.
Overall (operculum detached) - 78 (67) 56 μm × 94 (77) 63 μm
Specimens Measured: 29
Remarks: The main characteristic features of this species are its very fine, dense spines and the close spacing of its antapical protrusions. The spines are delicate and can occasionally be linked laterally by cross-bars, although never forming a complete distal reticulum as in Canningia.
Tabulation may be partially marked by penitabular alignment of spines, and this can be enhanced by some mesotabular reduction or loss of ornament so that some pandasutural areas can be clearly seen, particularly on the dorsal surface. This is an uncommon feature, however.
This species is a valuable marker for the latter part of the early Hauterivian; it was recorded between Speeton Beds C9A and C7B, upper regale to inversum ammonite Zones.