Artostrobus annulatus

(Bailey)

Cephalis cup-shaped, poreless, with a thin apical horn. Thorax cylindrical, with circular (proximally) to subrectangular (distally) pores in transverse rows, increasing in size toward the base. Shell height: up to 160 µm.

Ref.: Riedel (1958), Petrushevskaya (1967).

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