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Bicornus obscurus
Original description Duxbury, 2024:
Plate 4, Figures 7-9, 11-13, 15, 16
Holotype: Plate 4, Figures 11, 15
Paratype: Plate 4, Figures 12, 13
Type Locality: Vergol outcrop, early Valanginian, pertransiens ammonite Zone, premolicus Sub-zone, Holotype: Bed B151M, Slide B151M/1b, E.F. D47.0. Paratype: Bed B138M, Slide B138M/2, E.F. V33.1.
Derivation of Name: From the Latin obscurus, indistinct - in reference to the vestigial tabulation of this species.
Diagnosis: As for the genus.
Dimensions: Holotype 76 × 53 μm.
Paratype 91 × 58 μm.
Overall 91 (73) 51 μm × 58 (52) 43 μm.
Specimens measured – 11.
Remarks: The apical horn of Bicornus obscurus varies considerably in length, from being equal to the short antapical horn to being a much longer and stronger feature. In some specimens there appears to be a slight offset of the antapical horn, suggesting that it may be a left antapical feature, with the right antapical suppressed.
Tabulation is present but vestigial, although cingular and hypocystal ridges are usually present, outlining an indistinct pattern. Lateral cingular notching is a common feature.
A large hole occurs over much of the dorsal hypocyst and this suggests itself as a substantial medial thinning of the cyst in transmitted light. Which plates are involved in this feature is unclear but presumably 3" and 4"', together with a part of the cingulum. Negative images of the holotype and paratype are included in Pl. 4, Figs. 13, 15 in order to better illustrate the partial tabulation and dorsal hole.
Bicornus obscurus n. gen. n. sp. was observed only towards the base of the early Valanginian at Vergol, between Beds B138M and B151M, restricted to the pertransiens ammonite Zone, premolicus Sub-zone. However, Monteil (pers. comm.) has, "never observed this species in the Valanginian, pertransiens/premolicus Sub-zone" but he did record it (Monteil 1986) from the late Berriasian of the Val de Fier East section (Jura). This discrepancy is unresolved.
Plate 4, Figures 7-9, 11-13, 15, 16
Holotype: Plate 4, Figures 11, 15
Paratype: Plate 4, Figures 12, 13
Type Locality: Vergol outcrop, early Valanginian, pertransiens ammonite Zone, premolicus Sub-zone, Holotype: Bed B151M, Slide B151M/1b, E.F. D47.0. Paratype: Bed B138M, Slide B138M/2, E.F. V33.1.
Derivation of Name: From the Latin obscurus, indistinct - in reference to the vestigial tabulation of this species.
Diagnosis: As for the genus.
Dimensions: Holotype 76 × 53 μm.
Paratype 91 × 58 μm.
Overall 91 (73) 51 μm × 58 (52) 43 μm.
Specimens measured – 11.
Remarks: The apical horn of Bicornus obscurus varies considerably in length, from being equal to the short antapical horn to being a much longer and stronger feature. In some specimens there appears to be a slight offset of the antapical horn, suggesting that it may be a left antapical feature, with the right antapical suppressed.
Tabulation is present but vestigial, although cingular and hypocystal ridges are usually present, outlining an indistinct pattern. Lateral cingular notching is a common feature.
A large hole occurs over much of the dorsal hypocyst and this suggests itself as a substantial medial thinning of the cyst in transmitted light. Which plates are involved in this feature is unclear but presumably 3" and 4"', together with a part of the cingulum. Negative images of the holotype and paratype are included in Pl. 4, Figs. 13, 15 in order to better illustrate the partial tabulation and dorsal hole.
Bicornus obscurus n. gen. n. sp. was observed only towards the base of the early Valanginian at Vergol, between Beds B138M and B151M, restricted to the pertransiens ammonite Zone, premolicus Sub-zone. However, Monteil (pers. comm.) has, "never observed this species in the Valanginian, pertransiens/premolicus Sub-zone" but he did record it (Monteil 1986) from the late Berriasian of the Val de Fier East section (Jura). This discrepancy is unresolved.