S97

Notes on the Genera Stylodictya, Porodiscus and Stylochlamydium.

The following species are abundant, but their identification is difficult. Their morphological characteristics are frequently gradational and incomplete specimens are numerous. According to some classification schemes rotation of the specimen is necessary to confirm the specific identification; clearly this is impossible when counting specimens in a fixed slide.

Kozlova (in Petrushevskaya and Kozlova, 1972) presented a useful generic revision based primarily on the nature of the central structure. Her taxonomy is used herein where possible. In some instances familiar specific names are retained even if they are technically questionable. Species are illustrated and described from "ideal" specimens and in practice might have to be combined for counting purposes. Incomplete specimens may have to be grouped as gen. sp. indeterminate.

S99

Genus Stylodictya Ehrenberg 1847, emend, Koslova, 1972

"Stylodictya Ehrenberg, 1847 b. p 54 (part.); Porodiscus Haeckel, 1881, p. 491 (part); Staurodictya Haeckel 1881, p. 506 (part.); Stylodictya Haeckel, 1881, p. 509 (part.) Type species Stylodictya gracilis Ehrenberg, 1854a, p .246 .

Skeleton is flat or slightly concave with round outline; consists of equatorial and sagittal girdles (frontal girdle is not developed), wings of the rings are displaced at 45 degrees in relation to the main axes; at their merging point they do not envelope each other and thus form girdles or regular round or scalloped form, especially distinctive in the first systems. The first system is close to Tholostaurus (cupolas do not overlap each other), diameter approx. 30-40 microns, not submerged into the skeleton; the distance between systems is greater than or equal to the diameter of the central chamber.

"The main and additional spines are well developed and often extend as external spines. Rim of the disc is smooth with 4, 8, or more spines.

"Differs from Tholodiscus new gen. by the annular character of the wing connection, by the absence of the zig-zag radial lines in the plane of the disc, and by its more regular round outline.

Eocene-Recent". (from Petrushevskaya and Kozlova, 1972).

Note: central structure clearly visible

Species included: Stylodictya aculeata Jorgensen

Stylodictya validispina Jorgensen