Shandongidium retirugosum Xu Jinli et al., 1997, p.57, pl.6, figs.3–4,5a–b,8 ex He Chengquan et al., 2009, p.664. Holotype: Xu Jinli et al., 1997, pl.6, fig.8. This name was not validly published in Xu Jinli et al. (1997), since no English or Latin description was provided; He Chengquan et al. (2009, p.664) validated the name by publishing an English diagnosis. Age: middle-late Eocene.