R Pusillum Guide
Credit: Marina Potapova
  1. Valve linear to linear-elliptical
  2. Raphe straight, without distinct terminal raphe fissures
  3. Striae unseriate, slightly radiate throughout both valves
  4. One or two striae in the center of the raphe valve more broad than the other striae

Valves are linear to linear-elliptical or linear-lanceolate with rounded ends. The terminal raphe fissures are not distinct. The striae are uniseriate, with 4-5 areolae per stria, and slightly radiate throughout both valves.