From Fensome et al., 2019:

Fistulacysta, Davey, 1988, p.37.
Type: Davey, 1988, pl.8, fig.3, as Fistulacysta simplex.

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Original description: [Davey, 1988]:

Diagnosis:
Shape: The body is elongate in shape with rounded apical and antapical apices.
Wall: The cyst is apparently two layered with the outer wall forming crests. The surface is smooth to scabrate.
Paratabulation: The crests are sutural and especially well developed in the pre- and postcingular regions. The cingular region is defined mainly by a lack of ornamentation.
Archaeopyle: An apical archaeopyle is developed by the detachment of the apical plates (Type tA). The archaeopyle has a zigzag margin.

Affinities:
The combination of elongate body, apical archaeopyle, sutural crests and paucity of cingular ornamentation differentiates Fistulacysta from all previously described genera. Egmontodinium Gitmez and Sarjeant 1972 is somewhat similar but is ovoidal and has better developed crests which are obviously partly penitabular.

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Fensome, 1991, p. 227:

Remark:
Davey (1988, p.37) stated that the combination of elongate body, apical archeopyle, parasutural crests and paucity of paracingular ornament
differentiates Fistulacysta from all previously described genera. He compared Fistulacysta specifically with Egmontodinium Gitmez and Sarjeant, 1972.