The general absence of univalve mollusca in the white chalk is very marked. Of bryozoa there is an abundance, such as _Eschara_ and _Escharina_ (Figs. 257, 258). These and other organic bodies, especially sponges, such as _Ventriculites_ (Fig. 238), are dispersed indifferently through the soft chalk and hard flint, and some of the flinty nodules owe their irregular forms to inclosed sponges, such as Fig. 259, _a,_ where the hollows in the exterior are caused by the branches of a sponge (Fig. 259, _b_), seen on breaking open the flint. Fig. 257: Eschara disticha. White chalk. Fig. 258: Escharina oceani. White chalk. Fig. 259: A branching sponge in a flint, from the white chalk. The remains of fishes of the Upper Cretaceous formations consist chiefly of teeth belonging to the shark family. Some of the genera are common to the Tertiary formations, and some are distinct. To the latter belongs the genus _Ptychodus_ (Fig. 260), which is allied to the living Port Jackson shark, _Cestracion Phillippi,_ the anterior teeth of which (see Fig. 261, _a_) are sharp and cutting, while the posterior or palatal teeth (_b_) are flat (Fig. 260). But we meet with no bones of land-animals, nor any terrestrial or fluviatile shells, nor any plants, except sea-weeds, and here and there a piece of drift-wood. All the appearances concur in leading us to conclude that the white chalk was the product of an open sea of considerable depth. Fig. 260: Palatal tooth of Ptychodus decurrens. Lower white chalk. The existence of turtles and oviparous saurians, and of a Pterodactyl or winged lizard, found in the white chalk of Maidstone, implies, no doubt, some neighbouring land; but a few small islets in mid-ocean, like Ascension, formerly so much frequented by migratory droves of turtle, might perhaps have afforded the required retreat where these creatures laid their eggs in the sand, or from which the flying species may have been blown out to sea. Of the vegetation of such islands we have scarcely any indication, but it consisted partly of cycadaceous plants; for a fragment of one of these was found by Captain Ibbetson in the Chalk Marl of the Isle of Wight, and is referred by A. Brongniart to _ Clathraria Lyellii,_ Mantell, a species common to the antecedent Wealden period. The fossil plants, however, of beds corresponding in age to the white chalk at Aix-la-Chapelle, presently to be described, like the sandy beds of Saxony, before alluded to (p. 293), afford such evidence of land as to prove how vague must be any efforts of ours to restore the geography of that period.