The Gasteropoda are represented in past time from the Lower Silurian rocks up to the present day. Of the Branchifera the Holostomata are more abundant in the Palaeozoic period, the Siphonostomata abounding more in the Secondary and Tertiary rocks, but not attaining their maximum till the present day. The place of the carnivorous Siphonostomata in the Palaeozoic seas appears to have been filled by the Tetrabran-chiate Cephalopods. The Branchiate Gasteropods of fresh water are chiefly represented as fossils by the genera Melania, Paludina, Valvata, and Ampullaria.
The Heteropoda are likewise of very ancient origin, having commenced their existence in the lowest Silurian deposits. The genera Bellerophon, Porcellia, Cyrtolites, and Maclurea, are almost exclusively Palaeozoic; Bellerophina is found in the Gault (Secondary), and Carinaria has been detected in the Tertiaries.
The Pulmonate Gasteropoda, as was to be anticipated, are not found abundantly as fossils, occurring chiefly in lacustrine and estuarine deposits, in which the genera Limnaea, Physa, Ancylus, etc, are amongst those most commonly represented. These, however, are entirely Mesozoic and Kainozoic. In the Palaeozoic period the sole known representatives of the Pul-monifera are the Pupa vetusta, Pupa vermilionensis, Dawsonella Meeki, and Zonites priscus of the Carboniferous rocks.