Plate P4. Scale bar = 10 µm. 1-3. Helicosphaera paleocarteri (Sample 189-1171C-20X-6, 15 cm); (1) phase-contrast light (Ph); (2) differential-interference contrast light (DIC); (3) polarized light (XP). 4-7. Helicosphaera compacta; (4, 5) Sample 189-1168A-41X-5, 2 cm; (4) Ph; (5) XP; (6, 7) Sample 189-1168A-44X-2, 80 cm; (6) DIC; (7) XP. 8-10. Helicosphaera obliqua (Sample 189-1168A-28X-5, 15 cm); (8) Ph; (9) DIC; (10) XP. 11, 12. Helicosphaera perch-nielsenae (Sample 189-1168A-46X-7, 15 cm); (11) Ph; (12) XP.