Few American mollusks equal Helicina occulta Say in interest. It is an operculate species which has been reported at times as aquatic, though it is strictly terrestrial; its living representatives are distributed over widely separated areas in restricted local colonies, and evidently represent a declining race; and it is a common fossil of the loess of peculiar significance, of much more general distribution in the loess-covered portions of the upper Mississippi- Missouri basin, failing to reach the region of the northernmost living colonies, but extending well beyond them westward.
Proceedings of the Iowa Academy of Science
©1919 Iowa Academy of Science, Inc.
"Further Notes on Helicina occulta Say,"
Proceedings of the Iowa Academy of Science, 26(1), 385-390.
Available at: https://scholarworks.uni.edu/pias/vol26/iss1/37