Plate P2. Thalassiosira bipora f. prima Shiono. 1. Whole valve showing rimoportula (R) (Sample 186-1151A-60R-CC); light microscope (LM). 2. Whole valve showing R (Sample 186-1150B-10R-CC); LM. 3. External view of whole valve showing opening of R (Sample 186-1150B-6R-CC); scanning electron microscope (SEM). 4, 5. Sample 186-1151A-57R-CC; SEM; (4) external view of whole valve showing opening of R; (5) central area showing external openings of occluded areola (OC) and central fultoportula (CF). 6, 7. Sample 186-1151A-57R-CC; SEM; (6) internal view of whole valve; (7) central area showing internal openings of OC and broken CF.

Plate P2. Thalassiosira bipora f. prima Shiono. 1. Whole valve showing rimoportula (R) (Sample 186-1151A-60R-CC); light microscope (LM). 2. Whole valve showing R (Sample 186-1150B-10R-CC); LM. 3. External view of whole valve showing opening of R (Sample 186-1150B-6R-CC); scanning electron microscope (SEM). 4, 5. Sample 186-1151A-57R-CC; SEM; (4) external view of whole valve showing opening of R; (5) central area showing external openings of occluded areola (OC) and central fultoportula (CF). 6, 7. Sample 186-1151A-57R-CC; SEM; (6) internal view of whole valve; (7) central area showing internal openings of OC and broken CF.