Fig. 1 and 2.--Campilodiscus; a perfect frustule, and part of another, seen from above, Tertiary; Egra in Bohemia. _See ante_, p. 96. 3_a_.--Lituola nautilotdea. _Chalk, Chichester._ (By Mr. Walter Mantell.) Side view, × 8. 3_b_.--Front view of the last cell of 3d, to show the foramina with which it is pierced. 3_c_.--The last cell of 3_a_. 3_d_.--Side view of a young shell, before the produced, or straight part appears, × 20. 4_a_.--Flabellina Baudonina. _Chalk._ (M. D'Orbigny.) A young individual seen in profile, × 12. 4_b_.--The same, viewed laterally, shows the oblique arrangement of the cells. 5.--Nodosaria. _Chalk, Chichester._ (By Mr. Walter Mantell.) The line below indicates the natural size. ] [Sidenote: NODOSARIA. LITUOLA.] Nodosaria. _Lign. 111, fig. 5._--Straight, elongated cells placed end to end, separated by constrictions; the last formed cell has a round central aperture. Several beautiful species abound in the Chalk; specimens often occur adhering to the surface of the flint nodules. Nodosariæ are abundant in tertiary deposits. Mr. Walter Mantell discovered Foraminifera of this genus in the blue clay of Kakaunui, in New Zealand. Cristellaria. _Lign. 109, fig. 4._--The shell is in the form of a compressed Nautilus; it has a single aperture, which is situated at the angle of the keel; the cells are oblique. This genus comprises seventy fossil species, which occur in the Lias, Oolite, and Chalk. Living species are abundant in almost every sea. Flabellina. _Lign. 111, fig. 4a_.--In a young state, this shell, like the preceding, resembles that of a Nautilus, and the cells are oblique; but in the adult, are of a zigzag (chevron) form. It has a single round aperture. _Fig. 4a_ shows a young individual, seen in profile; _fig. 4b_ a lateral view, exhibiting the obliquity of the cells. Species of Flabellina are often found in cretaceous strata. The genus is not known in a recent state. Polystomella.--In its general form this genus resembles the other nautiloid shells above described, but its structure differs essentially; for there are several apertures along the side of the shell, as well as the opening in the last segment. The cells are simple, and each is a single cavity. The figures and details of structure, given by Professor Williamson, must be referred to, for an insight into the organization of this beautiful and complicated type of Foraminifera.[319] One species of Polystomella is said to occur in the Chalk; I have not detected this genus in our cretaceous deposits. Recent species swarm in our seas; and may be easily obtained from the mud and sand on the shores at Brighton.[320] [319] Trans. Microscop. Society, vol. ii. [320] Mr. Poulton has specimens of the shells, and the bodies of the animals deprived of the shell, mounted for the microscope.