Geissleria Ignota Guide
Credit: Rex Lowe
  1. Valves triundulate
  2. Central area expanded
  3. Striae radiate near center, becoming parallel near apices
  4. 2-3 rows of annulae

Valves triundulate with rostrate to subcapitate ends. The central area is expanded laterally with 2-4 shortened striae at the valve margin. Striae are radiate near the center of the valve, becoming parallel near the ends. Two to three rows of annulae are present at each apex of the valve.