From Williams et al., 2017:

[Arkellidinium, Beju, 1979, p. 1,4

Type species: Arkellidinium triapertum, Beju, 1979 (fig.1, no.1; figs.2A–A)]

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Original description: [Beju, 1979]:

Diagnosis:
Cavate dinocysts with subcircular to rounded polyhedral outline.
Endophragm broadly ovoidal to subcircular. Apical horn absent to weakly indicated, formed by the periphragm. Pericoel well developed on the hypocyst, especially around the antapex, reduced to absent on the epicyst and apical area. Endophragm attached to the periphragm on most of its ventral and dorsal surfaces. Both wall surfaces smooth to minutely ornate.
Peritabulation absent to weakly represented.
Pericingulum present, planar to slightly helicoidal.
Perisulcus present to vaguely indicated.
Archeopyle apical, including all apical paraplates;
a sulcal indentation is generally indicated.