Rossithidium pusillum has smaller valves, lower stria density, and more narrow axial area on the raphe valve.
Rossithidium petersenii has much larger central area on the raphe valve and a wider, rhomboid axial area on the rapheless valve.
Achnanthidium crassum has valves that are slightly arched. Striae on the raphe valve are radiate with greater stria density at the ends.