The Cerithiidæ are chiefly marine forms, some, however, entering brackish water. About five hundred fossil species have been described, some of them gigantic in comparison with any now living, of which more than two hundred are known.
Case 44.
The Scala scalaris was formerly considered a great rarity, as much as £40 having been given for a single specimen, which might now be purchased for as many pence.
Fig. 11.
Scala scalaris.
Case 44.
Cases 46–47.
The “Worm-shells” (Vermetidæ) are a very peculiar family. Their shells can scarcely be distinguished from the shelly tubes which are formed by certain species of marine worms, Serpula, &c. They are free and spiral in early life, but afterwards become distorted and generally attached to rocks, stones, &c. A foot for walking purposes therefore would be of no use; consequently it is more or less obsolete, serving only as a support to the operculum.
Case 48.
The “Screw-shells” (Turritellidæ) have elongate tapering shells; about 100 recent and 200 fossil species are known. One species only (Turritella communis) is now found living on the British coasts.
Case 49.