Encyonema minutum has smaller valves and higher stria density. Encyonema minutum var. pseudogracilis has larger valves, with lower stria density. Encyonema procerum has less strongly arched dorsal margins, a larger length to width ratio, shorter ventral striae and lower stria density.
BioData Reference
Krammer 1997 T1 Pl 6 Fig 19-27 Pl 25 Fig 1-10