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Helbydinium
From Williams et al., 2017:
[Helbydinium, Snape, 1992, p. 273
Type species: Helbydinium scabratum, Snape, 1992 (figs.6a,e)]
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Original description: [Snape, 1992]:
Diagnosis:
Cyst proximate, acavate with an ellipsoidal ambitus. An apical archaeopyle, type (tA), and accessory archaeopyle sutures are the only indications of paratabulation. There are six precingular paraplates with the parasulcal notch in the mid ventral position, presumably indicating a gonyaulacacean paratabulation. The wall is two-layered, the periphragm forming a non-paratabulate lamellar flange or crest; the layers are otherwise closely appressed. The flange is sagittal in position.
Affinities:
Fistulacysta has a similar shape, archaeopyle and wall relationship to Helbydinium, but differs in having parasutural crests. Belodinium and Boreocysta are also elongate ellipsoidal, have an apical archaeopyle and a two-layered wall structure. However, these genera differ in possessing a prominent apical horn with the former having a bicavate-circumcavate wall relationship, the latter having a holocavate wall.
[Helbydinium, Snape, 1992, p. 273
Type species: Helbydinium scabratum, Snape, 1992 (figs.6a,e)]
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Original description: [Snape, 1992]:
Diagnosis:
Cyst proximate, acavate with an ellipsoidal ambitus. An apical archaeopyle, type (tA), and accessory archaeopyle sutures are the only indications of paratabulation. There are six precingular paraplates with the parasulcal notch in the mid ventral position, presumably indicating a gonyaulacacean paratabulation. The wall is two-layered, the periphragm forming a non-paratabulate lamellar flange or crest; the layers are otherwise closely appressed. The flange is sagittal in position.
Affinities:
Fistulacysta has a similar shape, archaeopyle and wall relationship to Helbydinium, but differs in having parasutural crests. Belodinium and Boreocysta are also elongate ellipsoidal, have an apical archaeopyle and a two-layered wall structure. However, these genera differ in possessing a prominent apical horn with the former having a bicavate-circumcavate wall relationship, the latter having a holocavate wall.