Remarks: This is the least common species of Rugoglobigerina in the Upper Cretaceous of Western Australia; it occurs in the Santonian and basal Canipanian bed G of the Toolonga Calcilutite in the Murchison River area, and in the Gingin Chalk. Ten sinistrally coiled and six dextrally coiled specimens have been found, but this is not sufficient to indicate a preferred direction of coiling in this species.

Other described species of Rugoglobigerina have a preference for dextral coiling; Bronnimann (1952) observed only dextrally coiled specimens. Bolli, Loeblich, & Tappan (1957) stated that" All known species of Globotruncana and Rugoglobigerina tend to develop an almost exclusive preference for dextral coiling". Bolli (1951), investigating some Globorotalidae from Trinidad, found that random coiling is usually restricted to the early representatives of a species, whereas stratigraphically younger forms prefer a single direction, either dextral or sinistral.

It has not been possible to investigate the relative frequencies of the direction of coiling of the present species throughout their total range. The random coiling may indicate that these are early representatives of the species. By analogy with investigated lineages of planktonic foraminifera it is probable that a preferred direction of coiling would be developed by stratigraphically younger specimens.

Several subspecies of Rugoglobigerina have been established by Bronnimann (1952) in the Upper Cretaceous of Trinidad and by Gandolfi (1955) in the Upper Cretaceous of north-eastern Colombia. With more material and more detailed study it may be possible to recognise finer taxonomic divisions within the species here described from the Upper Cretaceous of Western Australia.

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