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Valensiella prenannus
Plate 17, Figures 3, 12-14
Holotype: Plate 17, Figure 3
Type Locality: Speeton Bed D2C, early Hauterivian, amblygonium ammonite Zone. Holotype: Slide D2C(1), E.F. G40.2.
Derivation of Name: This species appears to be the origin of Discorsia nannus (Davey 1974) Duxbury 1977, as discussed in Duxbury 2018.
Diagnosis: A small, thin-walled, ovoidal species bearing high, faintly striate crests, often with some microperforation. Large plates are outlined on the cyst surface by the linear crest bases, which can be vacuolar. Crestal margins are highlighted by thickening at or close to their distal edges. The archeopyle is apical and narrow, and the operculum is typically detached.
Dimensions: Holotype: 46 × 46 μm.
Overall (operculum detached) - 53 (44) 38 μm × 53 (43) 38 μm
Specimens Measured: 9
Remarks: This species is formally described here, in recognition of its stratigraphic value, having been informally discussed in Duxbury 2018. In the present study, Valensiella prenannus ranged no higher than Speeton Bed C9D. Including evidence from Duxbury 2018, the total range of this species is therefore late Berriasian, albidum Zone to early Hauterivian, regale Zone.
Valensiella prenannus has high, faintly striate sutural crests and superficially resembles Heslertonia striata (Eisenack and Cookson 1960) Norvick 1976. The latter species was described in Norvick 1976 (p. 47) as possessing a precingular archeopyle, which precludes its inclusion in Heslertonia Sarjeant 1966b emend. Duxbury 1980, a genus with an epicystal archeopyle. Intermediates between Valensiella prenannus and D. nannus show a gradual transition from high sutural crests to mesotabular tubular processes, maintaining faint longitudinal striations throughout (see Duxbury 2018).
Holotype: Plate 17, Figure 3
Type Locality: Speeton Bed D2C, early Hauterivian, amblygonium ammonite Zone. Holotype: Slide D2C(1), E.F. G40.2.
Derivation of Name: This species appears to be the origin of Discorsia nannus (Davey 1974) Duxbury 1977, as discussed in Duxbury 2018.
Diagnosis: A small, thin-walled, ovoidal species bearing high, faintly striate crests, often with some microperforation. Large plates are outlined on the cyst surface by the linear crest bases, which can be vacuolar. Crestal margins are highlighted by thickening at or close to their distal edges. The archeopyle is apical and narrow, and the operculum is typically detached.
Dimensions: Holotype: 46 × 46 μm.
Overall (operculum detached) - 53 (44) 38 μm × 53 (43) 38 μm
Specimens Measured: 9
Remarks: This species is formally described here, in recognition of its stratigraphic value, having been informally discussed in Duxbury 2018. In the present study, Valensiella prenannus ranged no higher than Speeton Bed C9D. Including evidence from Duxbury 2018, the total range of this species is therefore late Berriasian, albidum Zone to early Hauterivian, regale Zone.
Valensiella prenannus has high, faintly striate sutural crests and superficially resembles Heslertonia striata (Eisenack and Cookson 1960) Norvick 1976. The latter species was described in Norvick 1976 (p. 47) as possessing a precingular archeopyle, which precludes its inclusion in Heslertonia Sarjeant 1966b emend. Duxbury 1980, a genus with an epicystal archeopyle. Intermediates between Valensiella prenannus and D. nannus show a gradual transition from high sutural crests to mesotabular tubular processes, maintaining faint longitudinal striations throughout (see Duxbury 2018).