Portlandia ( Megayoldia ) thraciaeformis (Storer)
| 1960. | Portlandia (Megayoldia) thraciaeformis (Storer) Oyama, K. et al. 1960 p. 98, pl. 20, fig. 6a, b |
| 1958. | Portlandia (Megayoldia) gratiosa (Yokoyama) Makiyama, J. 1958 pl. 33, fig. 13 |
| 1925. | Yoldia gratiosa Yokoyama Yokoyama, M. 1925d p. 125, pl. 15, fig. 13 |
| Condition: | Present |
| Taxonomy: | Mollusca: Bivalvia: Yoldiidae: |
| Geologic Time: | Cenozoic: |
| Makiyama, J., 1958: Matajiro Yokoyama's Tertiary fossils from various localities in Japan. Part 2. Palaeontological Society of Japan, Special Papers, no. 4, pp. 1–6, pls. 25–57. (Reference No. 0368) |
| Oyama, K., Mizuno, A. and Sakamoto, T., 1960: Illustrated handbook of Japanese Paleogene molluscs., pp. 1–244, pls. 1–71. Geological Survey of Japan. (Reference No. 0412) |
| Yokoyama, M., 1925d: Mollusca from the Tertiary basin of Chichibu. Journal of the Faculty of Science, Imperial University of Tokyo, Section 2, vol. 1, pt. 3, pp. 111–126, pls. 14–15. (Reference No. 0476) |
 |
| Ichikawa, T., 1983, no. 9, p. 158. |
| Ichikawa, T., 1983, no. 9, p. 49. |
| Ichikawa, T., 1983, no. 9, p. 316. |
