In former periods, also, Mollusca were chiefly marine; fluviatile and terrestrial types occurring only in more recent periods.
Erodona and Himella are fluviatile forms from South America.
The species are, for the most part, marine, but a few of them belong to land and fluviatile genera.
Lacustrine and fluviatile deposits occur intermingled with the above.
It is a novel experience to us to glide along the still reaches among these fluviatile greenwoods.
I may notice here two other land shells, although they scientifically are grouped amongst the fluviatile Gasteropoda.
Their excavation by fluviatile action certainly dates back to a period long anterior to the advent of the Ice Age.
They have been carried away grain by grain by the denuding forces—by weathering, rain, frost, and fluviatile and marine action.
Among the fluviatile deposits, argillaceous marl beds now play an important part.
It lay some five feet beneath the surface in a deposit which seems to be an ancient one of fluviatile origin.