One of the largest rotation curve data bases of spiral galaxies currently available is that provided by Persic & Salucci (1995; hereafter, PS) which has been derived by them from unreduced rotation curve data of 965 southern sky spirals obtained by Mathewson, Ford & Buchhorn (1992; hereafter, MFB). Of the original sample of 965 galaxies, the observations on 900 were considered by PS to be good enough for rotation curve studies, and the present analysis concerns itself with these 900 rotation

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... ves. The analysis is performed within the context of the hypothesis that velocity fields within spiral discs can be described by generalized powerlaws. Rotation curve data was found to impose an extremely strong and detailed correlation between the free parameters of the power-law model, and this correlation accounts for virtually all the variation in the pivotal diagram. In the process, the analysis reveals completely unexpected structure which indicates that rotation curves can be partitioned into welldefined discrete subclasses.