Definition of "semiannular"

The capsule in both families is spherical, with a bistratose wall; the outer cell layer usually bears nodular thickenings […] ; the inner layer (of nearly equally large cells) lacks the regular semiannular or annular thickenings of most other leafy liverworts […]

1992, Rudolf M[athias] Schuster, The Hepaticae and Anthocerotae of North America: East of the Hundredth Meridian, volume V, New York, N.Y.: Columbia University Press, page 6