Shell white, inside and out, sometimes with a rusty or green¬ish stain here and there, and furnished with obsolete radiating ribs. Often attaining a length of from eight to fourteen inches.
Animal generally blackish, more or less marbled and streaked with white. Head, mantle edge and branchial lamella black. Head very long, not large in proportion ; muzzle small. Tentacles short, slender, pointed. Branchial lamellae not semicircular, as in most Patellae, but produced, twisted, and elongated, having, upon a superficial examination, an arborescent appearance. They are very slightly smaller in front. Radula with a well developed median tooth. Cusps of the teeth fawn color, with chestnut brown bosses and an orange ring at the point of insertion of the cusp.
Length: Up to 170 mm.

With large individuals often exceeding 200mm. in shell length the massive « Giant Mexican Limpet » is the largest of all living limpets. Ranging from western Mexico to Peru, it is the only Scutellastra species found in the eastern Pacific. An algae-grazing herbivorous gastropod living attached on hard substrates, it occurs from low tide to shallow subtidal waters down to about -10m. Although it used to be a comm.on species widely used as a local delicacy in dishes such as ceviche, overharvesting led to a great population decline and was apparent! close to extinction across parts of its range in Mexico. Today it is uncomm.on to rare at the typical shell length around 150mm. or less, large specimens exceeding 200mm. are very rarely found. It is said that the largest examples may attain a colossal 350mm. The shell is characteristically rostrated and oval-shaped, it is also exceptionally thick and can easily withstand an adult human being standing on it. Although large specimens appear featureless due to erosion and encrustation, it carries numerous major and minor dorsal radial ribs which is much more clearly seen in young individuals.

This magnificent limpet, the largest non-spiral gasteropod now living, proved, as might have been anticipated, to differ essentially from its smaller cousins. It is somewhat singular that the animal of a nearly white shell should be almost black, especially as the shell is an external one.

It is found in Central America.

Located at Barra de Navidad, Jalisco, Mexico