After the shell reaches 2½ whorls, the mantle resorbs the columella and septa of all the whorls except the body whorl. As a result, the viscera are no longer arranged in the spiral way usual in gastropods.
1: low ribs are all that are left of the resorbed septa that earlier separated the whorls of the spire.
2: remaining stump of columella.
3: most of septum (lower part) separating body whorl from spire.
4: rest of septum (upper part) separating body whorl from spire.

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