Crossword-Solution: UMBONAL 7 letters, 1 clue 🏆 scrabble score: 11

Right-hand scutum alone furnished with an internal umbonal tooth: uppermost part of peduncle dark-coloured.

King makes out five pairs and an odd one, and individualizes their respective functions as follows:--Three pairs are _lateral_, having their members limited to the sides of the shell; one pair are _transmedians_, each member passing across the middle of the reverse side of the shell, while the odd muscle occupies the umbonal cavity.

The _central_ and _umbonal_ muscles effect the direct opening and closing of the shell, the _laterals_ enable the valves to move forward and backward on each other, and the _transmedians_ allow the similar extremities (the rostral) of the valves to turn from each other to the right or the left on an axis subcentrically situated, that is, the medio-transverse region of the dorsal valve.

Its shell is considerably twisted just below the umbonal region, while its whole surface is densely striated.

The rounded valve, usually ornamented with radiating ribs, and the wing-like projections (called "ears"), from each side of the umbonal region, are never-failing characters.