Note 349 — Chapter XI
Reading edition
The form of the aperture does not necessarily indicate fresh-water genera. Melanopsis, Pirena, and most of the Melaniæ have a channelled or notched aperture. Fresh-water univalves frequently have the spire corroded; in a fossil state they can only be determined [to be fresh-water species] by their analogy to recent genera and sub-genera.—Note by Mr. Woodward.