Electron microscope, phase contrast, and dark field illumination analyses of Globigerinacea indicate that septal walls in both axial and horizontal sections are microgranular hyaline in character. The primary outer wall of Cretaceous Globigerinacea is microgranular hyaline, whereas Cenozoic Globigerinacea may have outer walls which are entirely microgranular hyaline, both radial hyaline and microgranular hyaline, or rarely, entirely radial hyaline. Mesopelagic forms of Globorotalia truncatulinoides, for example, possess an outer wall divided into (1) a radial hyaline 'calcite crust' composed of euhedral calcite prisms oriented with their C-axes normal to the surface of the test and (2) an inner laminated layer composed of heterogeneous microgranules of hyaline calcite.

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