Fig. 173.—Section of Shell of Turritella
Fig. 174.—Turritella communis and Cæcum trachea
In the succeeding shells, of the family Cerithiadæ, the spire is also considerably produced, so much so that some of the species closely resemble the Turret shells, but they are distinguished by usually having an expanded lip, at least in the adult form; and the mouth is channelled in front, and sometimes also behind. The animals of the group have short muzzles that are not retractile, the tentacles are wide apart, and the eyes are mounted on short pedicels. The median teeth are arranged in a single row, with three laterals on either side of each.
Fig. 175.—Cerithium reticulatum and Aporrhais pes-pelicani