DIMORPHOUS FORM.

GENUS Sagraina, D'ORBIGNY, emended by PARKER and JONES.

Early segments Uvigerine, later ones Nodosarian. Eocene to Recent.

EXAMPLE. S. striata, Schwager (Dimorphina), 'Novara-Exped., geol. Theil,' vol. ii. 1866, p. 251, pl. vii. fig. 99.

The typical Uvigerine commencement is distinctly seen in this species.

As a recent form S. striata seems confined to tropical areas, and ranges in its depth from quite shallow water to 350 fathoms. The fossil examples were obtained from the Eocene beds of Hungary, the Miocene of Malta, and the Pliocene of Kar Nicobar. Eocene to Recent. (Plate 11, fig. D.)

Test commencing with an imperfectly segmented series of chambers, sometimes resembling to a certain. extent the simpler forms of Polymorphina, to which genus the present group bears some affinities; afterwards branching irregularly and taking the form of subspherical chambers united by long and slender stoloniferous tubes, or a series of pyriform chambers with or without intermediate stoloniferous tubes.

GENUS Ramulina, RUPERT JONES.

Test branching, composed of spherical or pyriform

chambers connected by long stoloniferous tubes. Jurassic to Recent.

EXAMPLE.-R. globulifera, Brady.

This species, which may be taken as typical of the free-growing forms, is distinguished by its branching test, composed of irregular subglobular chambers, connected by slender curved or straight stoloniferous tubes, and which radiate from the chambers. Segments internally septate, but only in an imperfect manner. Texture hyaline, finely perforate. Surface of test hispid or aculeate, but not so coarsely as in the cretaceous species R. aculeata.

R. globulifera has been recorded as a fossil under various names from the Middle Jurassic of Poland and Switzerland, the Aptian beds of Surrey, the Gault of France and England, and from various Tertiary beds, as the London Clay, and the Pliocene of Italy. It occurs at moderate depths in the seas of the present day. Jurassic to Recent. (Plate 11, fig. E.)

GENUS Vitriwebbina, CHAPMAN.

Test adherent, consisting of a series of hemispherical or elliptical chambers, gradually increasing in size and usually arranged in a curvilinear manner. The commencing segment sometimes exhibits a polymorphine septation. Shell finely perforate, translucent or dull. Surface of the test smooth or minutely tuberculate. Aperture a simple crescentic space situated between the inferior margin of the shell

and its object of attachment, at the termination of the last chamber.

Cretaceous.

EXAMPLE.-V. lævis, Sollas sp. (Webbina), Geol. Mag.' Dec. 2, vol. iv. 1877, pp. 103, 104, pl. vi. figs. 1-3.

The test of this species is smooth and glossy in appearance. The segments, which are hemispherical or ovoid, are joined to form a short series; adherent to fragments of rolled phosphatic chips or shells, and usually found in hollows or recesses in such fragments, as if for protection.

V. lævis is found sparingly in various Cretaceous beds, as the Marl of New Jersey, the Gault of Folkestone, the Greensand of Cambridge, and the Chalkmarl of Kent. (Plate 11, fig. F.)

CHAPTER XIV

THE FAMILY GLOBIGERINIDE

THE group of Foraminifera which constitutes the above family is not, like most of the preceding divisions, separable into a closely connected and progressive series of forms, but the various genera have many features in common with the whole group, and the phenomena of isomorphism amongst species of different genera is often very marked. The greater number of the members of the GLOBIGERINIDE are pelagic or surface-living organisms.

The salient characters of the group are a test which is never attached; a perforate shell-wall very variable in thickness even in the same genus; chambers few, inflated, arranged spirally; aperture single or multiple, conspicuous. There is no supplementary skeleton nor canal system.

With regard to the isomorphism of the various species, mention may be made of Globigerina bulloides with Candeina nitida, Globigerina conglobata with Spheroidina bulloides and Pullenia obliquiloculata and Globigerina æquilateralis with Hastigerina pelagica and Pullenia quinqueloba. The genus Globigerina has some isomorphous types corresponding even with

certain forms of the next family, the RoTALIIDE, as Globigerina cretacea and Discorbina rugosa.

GENUS Globigerina, D'ORBIGNY.

Test coarsely perforate; trochoid, rotaliform, or symmetrically planospiral; segments few, inflated; pelagic specimens spinous. Cambrian to Recent.

EXAMPLES.-G. bulloides, D'Orbigny, Ann. Sci. Nat.' vol. vii. 1826, p. 277, No. 1; 'Modèles,' No. 17 and No. 76.

The size of the test in this species varies greatly. The British specimens are usually one-fifth the diameter of good typical examples from mid-ocean. It is found in every sea, and certain deep-sea deposits are often chiefly composed of the shells of this type-form. Undoubted examples are recorded from strata of Lower Cretaceous age, and it is well distributed throughout almost all Tertiary deposits up to the present time. The Pliocene specimens more nearly approach the recent examples in point of size.

Fig. H shows the appearance of the test when obtained from bottom oceanic deposits. (Plate 11, figs. H, h.)

G. bulloides, var. triloba, Reuss, Denkschr. d. k. Akad. Wiss. Wien,' vol. i. 1849, p. 374, pl. xlvii. fig. 11 a-e.

This is a three-chambered variety with an almost invisible spire, which is found associated with the typical G. bulloides. Fig. G represents a surface