Article: The micrometric formula and the classification of fenestrate cryptostomes

A critical assessment of the use of the micrometric formula in classifying fenestrate cryptostomes shows that although the device may be of some use as an aid to description and as a means of indexing species, it is an ineffective basis for structural comparisons. The method employed in making such comparisons is also unsound. Nevertheless, taxonomic conclusions are commonly drawn from them, and a result of this is an unreasonable increase in the number of recognized species. It is suggested that the micrometric formula should be discarded for comparative purposes and its place taken by one of the orthodox biometrical tests of significance. Such tests afford a simple and objective way of comparing sets of data. Samples for comparison should consist of groups of specimen means: owing to the colonial nature of the organisms, data from a single colony are inadequate for the purpose. A procedure for comparing samples is outlined, and an example given.