umbo
/ˈʌmbəʊ
/noun (plural umbones /ʌmˈbəʊniːz/ or umbos)
1 historical The central boss of a shield.The nearly spherical cones have eight to 10 scales, each looking like a shield with a central projection (called an umbo, if you want to impress your botanist or Scrabble-playing friends).
2 Biology A rounded knob or protuberance.
2.1 Zoology The highest point of each valve of a bivalve shell.The new species is characterized by a transversely extended, strongly biconvex to globular shell with prominent umbones, relatively numerous costae and a notothyrial cavity supported dorsally by a short median ridge....
- Argonauta attaches the egg-mass to the umbo of the shell near the dorsal arms, not in the mantle cavity or posterior parts of the shell.
- Below the umbones, the shell margin is folded inward forming a deep lunula and gaping between both valves.
2.2 Botany A central swelling on the cap of a mushroom or toadstool.
Derivatives
umbonal
- Cyzicus having elongate valves; umbo convex; dorsal margin straight; posterior margin slightly flared; growth bands widely spaced in umbonal region, more closely spaced elsewhere.
- The umbonal angle narrows while the shape remains mytiliform and the ‘lunule’ (byssal invagination) remains shallow.
- Hinge articulation either limited to overlapping shell margins on dorsal side of byssal invagination or consisting of a transposable tooth and socket developed on the umbonal septum.
umbonate
- M. oreades has a white spore print, adnate, adnexed or even free gills usually white to pale tan in colour, a mid-sized bell-shaped cap but can later become umbonate as it ages.
- Other decorative British products of this period include ‘umbonate’ disc brooches.
- An umbonate colony is elevated more in the center of the colony than the rise across the surface of the colony.
Origin
Early 18th century: from Latin, 'shield boss'.