1861
Orthis elegantula Hising. — Eichwald, pp. 237
1861
Orthis crassa sp. nov. — Lindström, pp. 369, fig. 13:11
1974
Isorthis crassa (Lindström, 1861) — Bassett & Cocks, pp. 10
1975
Isorthis (Arcualla) crassa — Walmsley & Boucot, pp. 80, fig. 7:16-23
1984
Isorthis crassa (Lindström, 1861) — Rubel et al., pp. 7
2011
Isorthis crassa (Lindström, 1861) — Rubel, pp. 46, fig. 27:19