Eunotia bidens is similar in shape and dimensions to E. richbuttensis; however, E. bidens valves have a lower areola density, ventral undulations, and subcapitate ends. While similar in shape to E. superbidens, valves of E. bidens differ by smaller breadth at the valve center and ends. In contrast to E. praerupta, E. bidens has more narrow valves and a higher stria density. Eunotia diodon is similarly biundulate on the dorsal margin, but E. bidens differs by less valve curvature and a lower areola density.