Calyptrosphaeraceae (this is an artificial grouping -heterococcolith phase is currently un-confirmed)
Kleijne (1991) p. 52, pl. XII.
After Young et al. 2003. BCs tube simple, with 2-layered wall; distal surface open except low, narrow, slightly oblique, s-shaped, bridge. Liths ca. 1.5 μm long.
CFCs bridge extended into leaf.
After Young et al. Rather variable morphotypes are assigned to C. gracilis and it may prove to include several discrete species, see Cros & Fortuno (202).