Type species: Bicornus obscurus n. gen. n. sp.

Derivation of Name: From the Latin bi-, two and cornus, horn – in reference to the characteristic spindle shape.

Diagnosis: Spindle-shaped, dorso-ventrally flattened dinocysts composed of autophragm only. A distally rounded apical projection of variable length and a single short, acuminate antapical projection are invariably present. Wall surface smooth to very finely granular with indistinct tabulation marked by narrow, low ridges. No clear archeopyle observed but a large hole is present over much of the dorsal surface, presumed to involve at least plates 3" and 4"'; much of the dorsal cingulum is absent.

Remarks: The taxonomic affinity of this genus is unclear. It may be gonyaulacacean, but if so its lack of a clear archeopyle and the presence of an acuminate antapical horn are atypical, the latter perhaps being more typical of peridiniacean taxa. The large hole over much of the dorsal surface may represent the archeopyle but, if so, the involvement of part of the dorsal hypocyst is again unusual.