The Brown Baby Ear, Sinum maculatum (Say, 1831), a member of the Moon-snail family Naticidae. It measures up to 1.2 inches and is similar in shell shape and size to its sister species, the White Baby Ear, Sinum perspectivum. Both species are present along the coast of Southwest Florida; both share the "open" shell with broad aperture, typical of the genus Sinum, and are not capable of fully withdrawing into their shells.
The Brown Baby Ear, however, is less commonly found, has a "taller" shell (its apex is more elevated), and displays brownish tinges on the outer shell surface.
The Brown Baby Ear, Sinum maculatum, from Sanibel Island. Photos by José H. Leal.