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Xenascus yunii
Xenascus yunii Prince et al., 2008, p.91–92, pl. 2, fig.8,9.
Holotype: Prince et al., 2008, pl.2, fig.8.
Age: middle Santonian.
Original description (Prince et al., 2008)
Holotype: Slide PRC 1475, PGW 12, E/F ref. D40/1.
Paratype: Slide PRC 1448, KGD 17, E/F Z18/2 (from Kingsdown Cliffs, east Kent).
Repository: Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, Wales, UK.
Type locality: Pegwell West Cliff, Kent, England.
Stratigraphic horizon: Basal middle Santonian, upper M. coranguinum Zone.
Etymology: Named in honour of Hye-Su Yun who has worked on the lower Santonian in Westphalia, Germany.
Diagnosis: A species of Xenascus that has an elongate antapical horn that connects to the central body only at the apex (as opposed to the hypocyst in X. perforatus). The lateral horn is also very elongate. The central body is elongate oval in shape.
Description: The central body is elongate oval in shape and relatively thin walled. The ornament consists of patches of rounded reticulations, similar to those observed on the illustrated specimens of Xenascus perforatus ( Vozzhennikova, 1967). The outer body is closely appressed to the inner body except at the bases of the antapical horn, lateral horn and other scattered processes; it appears to be smooth. The antapical horn is very elongate and narrow over most of its length; the sides being almost parallel except where it joins to the central body where it widens slightly. The lateral horn is also narrow and elongate and is sometimes attached to the inner body at 90 degrees to the antapical body, being bent and curved towards the antapical horn at around half its length. Both the antapical and lateral horns show perforations at the tips, which appear to be less damaged than those seen in X. perforatus, although they are probably of the same origin.
Other processes and spines, typical of those seen in other Xenascus species, arise from the outer body. The archaeopyle, type tA, shows a well-developed zigzag margin. No other paratabulation has been observed.
Dimensions: Holotype: central body 45 µm wide × 51 µm long; lateral horn 16 µm wide × 84 µm long; antapical horn 28 µm wide × 97 µm long; maximum process length 24 µm. Range of 8 measured specimens: central body 40–68 µm (average 49 µm) wide × 30–61 µm (average 48 µm) µm long; overall (including processes) 40–88 µm (average 52 µm) wide × 82–170 µm (average 136 µm) long; lateral horn 5–8 µm (average 6 µm) wide × 61–86 µm (average 77 µm) long; antapical horn 20–32 µm (average 28 µm) wide × 52–100 (average 84 µm) long; maximum process length 12–24 µm (average 19 µm).
Comparison: Differs from Xenascus perforatus by the closely appressed wall layers and the narrower antapical horn which, because of the smaller width, appears to be longer. Xenascus ceratioides has a larger, wider, better developed antapical horn and a shorter lateral horn. According to the dimensions given in Yun (1981), X. sarjeantii is smaller than X. perforatus and lacks the elongate horn.
Holotype: Prince et al., 2008, pl.2, fig.8.
Age: middle Santonian.
Original description (Prince et al., 2008)
Holotype: Slide PRC 1475, PGW 12, E/F ref. D40/1.
Paratype: Slide PRC 1448, KGD 17, E/F Z18/2 (from Kingsdown Cliffs, east Kent).
Repository: Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, Wales, UK.
Type locality: Pegwell West Cliff, Kent, England.
Stratigraphic horizon: Basal middle Santonian, upper M. coranguinum Zone.
Etymology: Named in honour of Hye-Su Yun who has worked on the lower Santonian in Westphalia, Germany.
Diagnosis: A species of Xenascus that has an elongate antapical horn that connects to the central body only at the apex (as opposed to the hypocyst in X. perforatus). The lateral horn is also very elongate. The central body is elongate oval in shape.
Description: The central body is elongate oval in shape and relatively thin walled. The ornament consists of patches of rounded reticulations, similar to those observed on the illustrated specimens of Xenascus perforatus ( Vozzhennikova, 1967). The outer body is closely appressed to the inner body except at the bases of the antapical horn, lateral horn and other scattered processes; it appears to be smooth. The antapical horn is very elongate and narrow over most of its length; the sides being almost parallel except where it joins to the central body where it widens slightly. The lateral horn is also narrow and elongate and is sometimes attached to the inner body at 90 degrees to the antapical body, being bent and curved towards the antapical horn at around half its length. Both the antapical and lateral horns show perforations at the tips, which appear to be less damaged than those seen in X. perforatus, although they are probably of the same origin.
Other processes and spines, typical of those seen in other Xenascus species, arise from the outer body. The archaeopyle, type tA, shows a well-developed zigzag margin. No other paratabulation has been observed.
Dimensions: Holotype: central body 45 µm wide × 51 µm long; lateral horn 16 µm wide × 84 µm long; antapical horn 28 µm wide × 97 µm long; maximum process length 24 µm. Range of 8 measured specimens: central body 40–68 µm (average 49 µm) wide × 30–61 µm (average 48 µm) µm long; overall (including processes) 40–88 µm (average 52 µm) wide × 82–170 µm (average 136 µm) long; lateral horn 5–8 µm (average 6 µm) wide × 61–86 µm (average 77 µm) long; antapical horn 20–32 µm (average 28 µm) wide × 52–100 (average 84 µm) long; maximum process length 12–24 µm (average 19 µm).
Comparison: Differs from Xenascus perforatus by the closely appressed wall layers and the narrower antapical horn which, because of the smaller width, appears to be longer. Xenascus ceratioides has a larger, wider, better developed antapical horn and a shorter lateral horn. According to the dimensions given in Yun (1981), X. sarjeantii is smaller than X. perforatus and lacks the elongate horn.