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Cribroperidinium aequum

Cribroperidinium? aequum (Mao Shaozhi and Norris, 1988) Lentin and Williams, 1989

Originally Millioudodinium?, subsequently (and now) Cribroperidinium?.
At the time of the transfer, Lentin and Williams, 1989, questionably include this species in Cribroperidinium.
Holotype: Mao Shaozhi and Norris, 1988, pl.2, fig.17
Locus typicus: Kukebai Formation, Wuluokeqiate section, China
Stratum typicum: Late Cretaceous

Original diagnosis: Mao Shaozhi and Norris, 1988, p.35: Millioudinium aequum
Cyst proximate, typically of intermediate size (50 Ám), spherical with a small prominent apical horn. Autophragm thin, readily folding along cyst margin.
Tabulation gonyaulacacean, indicated by low sutural ridges; faint, veinlike low ridges between sutural ridges masking some details of tabulation. Archeopyle precingular, type (P)a, formed by loss of 3"; operculum typically attached along part of sides with 2" and/or 4", sometimes indiscernible. Cingulum helicoid.

Original description: Mao Shaozhi and Norris, 1988, p. 35: Millioudinium aequum
Cyst spherical to broadly spherical. Apical horn small but pointed, commonly 2 to 5 Ám long. Antapex rounded, lacking horns or prominences. Specimens randomly oriented because of sphericity, folding readily because of thin wall. Cingulum levorotatory, usually 3 to 4 Ám wide, bounded by ridges less than 0.5 Ám high. Sulcus extending from cingulum towards antapex. Sutural ridges indistinct; possible tabulation formula of 4", ?la, 6", Xc, 6""", 1p, 1"""", if determinable. Surface between sutural ridges covered with incomplete, faint, slightly sinuous low ridges, giving the thin autophragm a veinlike reticulate appearance. Omphalos often darker in colour, spherical to subspherical in shape. Dimensions: Length 55 to 75 Ám (holotype 70 Ám), width 62 to 71 Ám (holotype 70 Ám).

Affinities:
Mao Shaozhi and Norris, 1988, p. 35: Millioudinium aequum
Millioudodinium (?) aequum closely resembles M. (?) venulosum but differs in having a spherical rather than an elongate cyst. Text-Figure 9 shows almost no intermediate forms between them. As with M. (?) venulosum, the generic assignation is questionable to Millioudodinium rather than Cribroperidinium because of the imperfect microreticulate low ridges (which are not certainly accessory ridges typical of Cribroperidinium) and the lack of detailed information on tabulation.
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