Pleistocene specimens were described and plating diagrams given by Nisiyama (1968). Fibulariella differs from Fibularia principally in characters not associated with test structure. Fibulariella has a plated peristome and periproctal plates are small and numerous whereas Fibularia has a naked peristome and five valve-like periproctal plates. The pedicellariae are also distinctive, being bidentate in Fibulariella and tridentate in Fibularia. Finally Fibulariella has three calcite rods in its suckered tube feet whereas Fibularia lacks such rods. The elongate periproct is distinctive but probably not a very reliable character (in the illustrated specimen from Shigei 1986, the periproct is effectively circular).
Cyamidia is possibly a senior synonym of this genus, because of its elongate periproct and lack of internal buttressing. However, without information on its periproctal and peristomial plating there can be no certainty and Cyamidia is best left as incertae sedis.
Nisiyama, S. 1968. The echinoid fauna from Japan and adjacent regions, Part II. Palaeontological Society of Japan, Special Paper 13, 1-491, pls 19-30.
Shigei, M. 1986. The echinoids of Sagami Bay Maruzen Co, Tokyo.