Guide to Ulnaria acus
- Valves narrow-lanceolate
- Apices attenuated, subrostrate to subcapitate
- Central area present
- Rimoportulae present
Valves are narrow-lanceolate, often with subrostrate to subcapitate apices. The sternum is narrow, expanding to a central area where ghost striae often present. Rimoportulae are present at the apices.