How did it continue to produce eggs with calcareous shells on a calcium poor diet on a soil entirely lacking in limestone?

Their coiled, calcareous shell has a diameter of less than 1 cm.

Snails are hatched from eggs with calcareous shell about 5-7.3 months after laying.

Species in this superfamily have a calcareous, bilaterally symmetrical conical or globular shell.

When adult, they have a calcareous shell composed of several pieces.

They are generally more or less covered and protected by a calcareous shell, which may be univalve, bivalve, or multivalve.

As the calcareous shells of crustaceans who lived in the sea were discarded, they built up on the floor and eventually became calcium carbonate-limestone.

Most reptiles lay amniotic eggs covered with leathery or calcareous shells.

Its calcareous, heavily-ribbed, shell can grow to approximately 7 to 8 cm across.

They have a hard calcareous shell made of two parts or 'valves'.