The general morphology of Globorotalia (Turborotalia) praecentralis Blow, 1979, is similar in gross aspect to that of Globortalia (T.) centralis Cushman and Bermudez. However, praecentralis differs from centralis in possessing a more tightly expressed coiling-mode, more embracing and more closely appressed chambers as seen in dorsal aspect especially, as well as in having a proportionately smaller umbilicus and less widely open aperture. Whereas, in G. (T) centralis, the mural-pores are generally of the same dimensions (proportionately) as they are in praecentralis, the latter form usually has distinct pore-pits present on the surfaces of the earlier chambers. On the other hand, the morphotypes referable to centralis have only very small pore-pits without distinct inter-pore ridges. Nevertheless, in praecentralis the last (or latter) chamber usually shows the absence of pore-pits even when they are strongly developed in the earlier chambers (cf. figs. 8 and 9, also figs. 1, 5, and 6). G. (T) praecentralis evolves slowly and gradually into G. (T.) centralis within the interval of Zone P.11 and this morphogenesis involves only the relaxation of the coiling-mode and the gradual reduction of the pore-pits both in size and density. . . .

"Whilst G. (T.) praecentralis is directly ancestral to G. (T) centralis, the morphotype is also phylogenetically ancestral to G. (T.) pseudomaveri Bolli, 1957. Thus, G. (T) pseudomayeri retains the tight coiling-mode seen in praecentralis but adopts a somewhat higher spire and a shallow, almost closed, umbilicus (cf. Bolli, 1957, U. S. Nat. Mus., Bull., no. 215, pl. 37, figs. 17a-c, and the metatype figured herein on pl. 248, fig. 11). Furthermore, G. (T.) pseudomayeri not only has dorsally appressed and embracing chambers but the ventral side shows this feature to a greater extent than seen in praecentralis Blow, 1979. Again, the aperture in praecentralis is of the same general type as seen in centralis (but not quite so widely and evenly open both dorsally and proximally), however, in pseudomayeri, the aperture is a uniformly, lowly open, slit-like opening. Finally, pseudomaveri shows narrow wedge-like chambers in ventral aspect and sensibly equidimensional chambers as seen in dorsal aspect, as compared to the distinctly tangentially longer chambers seen in dorsal aspect of praecentralis. G. (T) praecentralis has less narrowly wedge-shaped chambers in ventral aspect as compared to those of pseudomaveri. In the paratypic suite of specimens figured in this work, the paratype illustrated in fig. 5 shows characters which connect the typical praecentralis to pseudomayeri Bolli. However, this specimen is still considered referable to praecentralis since, in particular, it possesses the more widely open aperture and less narrowly wedge-shaped chambers in ventral aspect as compared to those of pseudomayeri.

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