About Gibbula magus (Linnaeus, 1758)
The shell of Gibbula magus varies in size between 17 mm and 35 mm. This is an abundant species. The solid shell is widely and deeply umbilicate, with a low-conical shape. The shell's color varies greatly: it can be whitish or yellowish, marked with zigzag radiating stripes, blotches, or lines of pink or rich brown. Sometimes the markings are broken into tiny flecks that make the entire shell appear minutely mottled, and sometimes markings are completely absent. The base of the shell has radiating zigzag stripes. The apex is acute. The conical spire holds 7 to 8 whorls, which are swollen, gibbous, and radiately folded beneath the sutures, with a rim or flange at the periphery. The entire surface of the shell is finely spirally striated. The shell base is convex. The aperture is very oblique, shaped like a rounded rhomboid, and is smooth on the inside. The columella is oblique; its edge is straight or slightly convex in the middle, and is slightly reflexed over the umbilicus at its insertion. The umbilicus is bounded by a strong spiral rib. This species occurs in the North Sea, the North Atlantic Ocean around the Azores and Morocco, and in the Mediterranean Sea.
