The title of the _Gasteropoda_ is derived from two Greek words signifying _belly_ and _foot_; the _raison d’être_ of that title being that these animals progress by means of flattened discs placed under their bellies. The snail, slug, and cowrie, are leading types of this class. In the _Pteropoda_ (from Greek words signifying _wing_ and _foot_) locomotion is effected by membranous fins or wings. Lastly, the _Cephalopoda_ are so called because they have prominently, as a class, heads and feet, locomotion being effected by a set of tentacles (arms or legs, as you will). The cuttle‐fish and devil‐fish (or octopus) are types of this important series of animals. [Illustration: THE LIMPET (_Patella_).] The vastness of the subject precludes the possibility of details, and for evident reasons a few of those inhabiting the sea itself can only be considered here. Among the “Gasteropods,” as they are familiarly termed, the limpets constitute a numerous family. The scientific name _Patella_ (a deep dish or knee‐cap) was given to them by Linnæus, the form of their shells fully warranting the title. Some of them are oval, others circular; but all terminate in an elliptic cone. Otherwise they are varied enough, some being smooth, but others having ridges or scales on the outer surface, the edges being often dentated. Their colours are very varied. The head of the animal itself has two horns and two eyes; its foot is a thick fleshy disc, and when it means to hold on to a rock we all know how difficult it is to dislodge it, for the said foot becomes a kind of sucker. Some of those from the coast of Africa and the Antilles, &c., have elegant forms, as witness _Patella umbella_, _P. granatina_, _P. longicosta_, and others. Although often eaten, they are very tough and indigestible. In Southern seas they attain to a great size; for example, in the Straits of Magellan the natives use for culinary purposes species as large as a slop‐basin. [Illustration: TURBO.] [Illustration: TROCHUS.] Well‐known shells are also those of many species of _Trochus_; the spiral shell has literally a _spiral animal_ inside it. So also some of the fifty species of _Turbo_, which are often marbled in beautiful colours outwardly and superbly nacred within. So again the winding pyramidal shells of the _Turritella_, many of which are found in every sea. And once more, what mantelpiece of old was not adorned with a pair or more of cowrie shells (_Cypræ_), natives of every sea! They range from the little whitish money cowrie, actually used in place of coin in parts of Africa to‐day, to handsome shells of large size. The animal which inhabits this shell is elongated, and has a head with a pair of long tentacles, each having a very large eye. The foot, as one example specially will show (_Cypræ tigris_) is an oval sucker, capable of great tenacity. [Illustration: THE COWRIE (_Cypræa tigris_).]