Fig. 7D-E, (See Plate 3and 4)
Type species: Hystrichosphaeropsis ovum (Deflandre, 1935).

Derivation of name: Gulficum, from the locality where the taxon was first found.

Diagnosis: The cysts are circumcavate and present an apical horn and a precingular archeopyle (Stover and Evitt, 1978), indicating their assignment to Hystrichosphaeropsis.

Description: Circumcavate, ovoidal to ellipsoidal proximate dinoflagellate cyst with a precingular archeopyle type P (3″) and an apical horn with an acuminate tip. The apical horn is built by the extension of the periphragm. The endophragm is ovoidal and densely ornamented with small granules (less than 1 μm). The presence of low sutural septae defines tabulation, but it is not visible in the sulcal zone. Tabulation formula includes 4′, 6″, 6c, 6″’, 1p, 1″”. Sutural septae are smooth and elevated in the ventral part of the cysts and create an inflated shield structure and cavation in the ventral-antapical part of the cyst. Pre-cingular archeopyle is formed by losing the third precingular plate 3”.

Dimensions: Diameter of the cyst: wide: 34 μm, high: 45 μm. Height of dorsal sutural septae: 2–3 μm; height of ventral sutural septae: 8 μm; length of apical horn: 22 μm. Observed range: Diameter of the cyst: wide: 34–40 μm, high: 45–50 μm; height of ventral sutural septae: 2 μm; height of dorsal sutural septae: 8–16 μm; length of apical horn: 22–26 μm. Number of species measured: 6.

Differentiation: The granular endophragm and well-developed apical horn of H. gulficum differentiate this species from other species in this genus.

Type locality: Southern Gulf of Mexico, Campeche escarpment, offshore Yucatan peninsula, Site 94 DSDP-Leg 10.
Type level: Middle Eocene (505.5–502.5 mbsf).

Range: Occurrence in samples of the Middle Eocene (505.5–502.5 mbsf).