from The Century Dictionary and Cyclopedia
- n. In pathology, a cancer or carcinoma.
- n. 2. [capitalized] In zoology, a genus of brachyurous decapod crustaceans; the shore-crabs.
Sorry, no etymologies found.
The third option is the introduction of an alien species, the carcinus green crab, which might have caused the snails to make harder shells.