Alterbidinium ioannidesii, Pearce, 2010, p.66–67, pl.1, figs.1–6.

Holotype: Pearce, 2010, pl.1, figs.1–6.
Type locality and horizon: Trunch borehole, Norfolk, UK; 298.9–299.0 m, Burnham–Flamborough Chalk (undifferentiated), low Offaster pilula Zone (low lower Campanian).
Age: early Campanian.

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Original description: [Pearce et al., 2010]:

Diagnosis:
A species of Alterbidinium possessing a well-developed parasutural paratabulation on the periphragm

Description:
Medium-sized peridinioid, cornucavate to circumcavate dinoflagellate cyst. The wall is two-layered composed of a smooth endophragm and a finely reticulate to striate periphragm that forms low parasutural ridges with no accessories.
The pericyst is elongate ellipsoid to biconical and forms a well-developed apical and left antapical horn (right antapical horn much reduced or absent).
The endocyst is sub-spherical to ovoidal and lacks horns, follows the general shape of the pericyst and lacks supporting processes.
The paratabulation is indicated by well-developed parasutural crests indicating the formula: 4#, 3a, 7#, ?c, 5%, 2$$.
The paracingulum is indicated by parallel horizontal crests, and undifferentiated, except perhaps by the most posterior paraplate in contact with the right sulcal boundary.
The parasulcus is indicated by a deep longitudinal depression.
The periarchaeopyle is intercalary (Type I, operculum detached) and formed by the loss of a steno-deltaform 2a paraplate. The endo-archaeopyle type has not been identified.

Affinities/Comparison:
Differs from other species of Alterbidinium by possessing clearly developed parasutural crests on the periphragm.