retuse

Shell transversely oblong, thick, depressed, within purple; hinge plate thick, truncate, with an obsolete lamellar tooth in each valve; umbones retuse.

Shell oval, broad, thick; hinge margin subarcuated, the extremities winged and angulated; umbones prominent, the tips retuse.

Involucral leaves numerous, small, incised, those of the stem rounded or retuse.

Leaves entire or barely retuse.

Loosely and widely pinnate; leaves round, entire, opaque; lower lobe subrounded, cucullate, close to the stem; underleaves subquadrate, toothed at the anterior angles; involucral leaves with 2 or 3 entire lobes; perianth tuberculate, retuse.—Rocks and trunks of trees; rather common.