It was succeeded by the sessile-fruited oak, which was in turn supplanted by the pedunculate form of the same tree.
In Ulodendron the large circular, distichously arranged prints were supposed to have been formed by the pressure of the bases of sessile cones, though this interpretation of the scars is open to doubt, and it is now more probable that they bore deciduous vegetative branches; in the Halonial branches characteristic of the genus Lepidophloios the tubercles may perhaps mark the points of insertion of pedunculate strobili.
The vernacular name barnacle, traceable to the fable of pedunculate cirripedes hatching out into bernicle geese, has also been transferred to the sessile cirripedes, which are popularly known as acorn barnacles.
The bathymetric range of sessile as well as pedunculate forms down to such depths as twelve or eighteen thousand feet - Verruca quadrangularis, Hoek, 1900 fathoms; Sealpellum regium, Wyville Thomson, 2850 FIG.
Therein an order Thoracica comprehends the pedunculate Lepadidae, together with the operculate and sessile Balanidae and Verrucidae; a single species without cirrhi constitutes the order Apoda, and a single species with only three pairs of cirrhi the order Abdominalia.