Faint striae, composed of areolae that may not penetrate the valve wall.
Convex, rounded, protuberant; exceeding a semi-circle but less than a circle.
The view of the frustule when the girdle is uppermost. See
valve view for an
alternate view of the frustule and
cingulum for a definition
of the girdle.
A small rounded projection of silica on the outer surface of the valve.