From Fensome et al., 2019:
Subtilisphaera foliacea (Eisenack and Cookson, 1960, p.2, pl.1, fig.3) Stover and Evitt, 1978, p.239. Holotype: Eisenack and Cookson, 1960, pl.1, fig.3. Originally Deflandrea, subsequently Alterbia (combination illegitimate), thirdly (and now) Subtilisphaera. Age: Turonian–middle Senonian.

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Original description: Eisenack and Cookson, 1960, p.2: Deflandrea foliacea
Shell flat, broadly oval in outline, divided almost equally by a rather broad shallow girdle and narrowing towards a short blunt apical projection and one or occasionally two slight antapical prominences. A short, broad longitudinal furrow is developed on the central surface of the hypotheca. The capsule is approximately circular in outline and does not fill the shell laterally. A pylome has not bee observed. Shell-membrane thin, transparent, wall of capsule slightly granular.
Dimensions: Type--57 µm long, 48 µm broad. Range--53-67 µm long, 43-52 µm broad.

Affinities:
Eisenack and Cookson, 1960, p.2: Deflandrea foliacea
This species closely resembles D. rotundata but differs from it in the shape of the epitheca.