Fossils of the White Chalk.—Among the fossils of the white chalk, echinoderms are very numerous; and some of the genera, like _Ananchytes_ (see Fig. 239), are exclusively cretaceous. Among the Crinoidea, the _Marsupites_ (Fig. 242) is a characteristic genus. Among the mollusca, the cephalopoda are represented by Ammonites, Baculites (Fig. 229), and Belemnites (Fig. 226). Although there are eight or more species of Ammonites and six of them peculiar to it, this genus is much less fully represented than in each of the other subdivisions of the Upper Cretaceous group. Among the brachiopoda in the white chalk, the _ Terebratulæ_ are very abundant (see Figs. 243-247). With these are associated some forms of oyster (see Fig. 251), and other bivalves (Figs. 249, 250). Fig. 240: Micraster cor-angumum. White chalk. Fig. 241: Galerites albogalerus. White chalk. Fig. 242: Marsupites Milleri. White chalk. Fig. 243: Terebratulina striata. Upper white chalk. Fig. 244: Rhynchonella octoplicata. Upper white chalk. Fig. 245: Magas pumila. Upper white chalk. Fig. 246: Terebratula carnea. Upper white chalk. Fig. 247: Terebratula biplicata. Upper cretaceous. Fig. 248: Crania Parisiensis. Inferior or attached valve. Upper white chalk. Fig. 249: Peten Beaveri. Lower white chalk and chalk marl. Fig. 250: Lima spinosa. Upper white chalk. Among the bivalve mollusca, no form marks the Cretaceous era in Europe, America, and India in a more striking manner than the extinct genus _Inoceramus_ (_Catillus_ of Lam.; see Fig. 252), the shells of which are distinguished by a fibrous texture, and are often met with in fragments, having probably been extremely friable. Of the singular family called _Rudistes_ by Lamarck, hereafter to be mentioned as extremely characteristic of the chalk of southern Europe, a single representative only (Fig. 253) has been discovered in the white chalk of England. Fig. 251: Ostrea vesicularis. Upper chalk and upper greensand. Fig. 252: Inoceramus Lamarckii. White chalk. _Radiolites Mortoni_, Mantell. Houghton, Sussex. White chalk. Diameter one-seventh nat. size. Fig. 253. Two individuals deprived of their upper valves, adhering together. Fig. 254. Same seen from above. Fig. 255. Transverse section of part of the wall of the shell, magnified to show the structure. Fig. 256. Vertical section of the same. On the side where the shell is thinnest, there is one external furrow and corresponding internal ridge, _a_, _b_, figs. 255, 256; but they are usually less prominent than in these figures. The upper or opercular valve is wanting.