Sellaphora subbacillum, S. ventraloides and S. aggerica are similar in size, stria density, and the presence of grooves that are visible in LM. Sellaphora ventraloides has a more lanceolate valve outline and bow-tie-shaped central area. The valve ends of S. subbacillum and S. aggerica are broadly rounded - never subcapitate. The stria density is slightly higher in S. subbacillum and S. aggerica.