Phormocyrtis striata exquisita (Kozlova)

Podocyrtis exquisita Kozlova in Kozlova and Gorbovets, 1966, p.106, pl.17, fig.2

Phormocyrtis striata exquisita (Kozlova), Foreman, 1973, p.438, pl.7, figs.1-4, 7-8, pl.12, fig.5 (with synonymy)

DESCRIPTION

Shell as for Phormocyrtis striata striata, with the exception that the abdomen is triangular in transverse section with early forms frequently having keels at the angles of the triangle, and pores less regular in shape and arrangement (Foreman, 1973).

DIMENSIONS

Based on 20 specimens. Length overall, exclusive of horn, 150-220 µm; greatest width of abdomen 70-130 µm (Foreman, 1973).

DISTINGUISHING CHARACTERS

P. s. exquisita is distinguished from P. s. striata by its abdomen being concave-triangular in transverse section (Sanfilippo et al., 1985).

VARIABILITY

The abdomen is triangular in transverse section. Early forms frequently have keels at these angles and the pores are irregular in size and arrangement (Sanfilippo et al., 1985).

DISTRIBUTION

P. s. exquisita occurs in tropical assemblages of Paleocene to early Eocene age. Its morphotypic first appearance has not been determined. Its evolutionary transition to Phormocyrtis striata striata is approximately synchronous with the lower limit of the Phormocyrtis striata striata Zone.

PHYLOGENY

P. s. exquisita gave rise to P. s. striata, but its ancestor is unknown.