. Bulletin of the British Museum (Natural History) Geology Supplement. 24 SHELVE DISTRICT The number of individuals attributable to any species represented in the collection is small enough to warrant not only the invariable use of small sample techniques but, for many taxa, nothing more than the mean (or mode) and range of variability. Continuous univariate characters which are assumed to be normally distributed, like the distances at which folds originate anterior of umbones or the wavelengths of ribs at a given distance antero-medially of the umbo, have been compared by the Mest. Discontinu
. Bulletin of the British Museum (Natural History) Geology Supplement. 24 SHELVE DISTRICT The number of individuals attributable to any species represented in the collection is small enough to warrant not only the invariable use of small sample techniques but, for many taxa, nothing more than the mean (or mode) and range of variability. Continuous univariate characters which are assumed to be normally distributed, like the distances at which folds originate anterior of umbones or the wavelengths of ribs at a given distance antero-medially of the umbo, have been compared by the Mest. Discontinuous univariate characters, like the number of costae ornamenting valves or the relative branching of costellae enumerated according to Bancroft's notation (Bancroft 1945 : 186 ; Williams 1962 : 77), have been compared by x2 tests, or contingency or two-by-two tables dependent on the size of samples. Continuous variables derived by measuring the shell or its several parts, like the cardinalia, dental plates or muscle impressions, are expressions of incremental proportional growth, which may or may not be allometric, and all show very high positive (or rarely negative) correlations with one another. The significance of any differences in estimates of such parameters has been determined by statistical analysis of a series of bivariate distributions. The method is adequate for the comparison of such closely inter-related estimates of shell growth. It also has the advantage of not obscuring the identity of those characters that underwent changes in the rate of growth during cladogenetic or phylogenetic speciation. The development of sig- nificantly longer dental plates in one of a number of compared species, for example, will be apparent whether the lengths of plates are consistently paired with the lengths, maximum widths or depths of the pedicle valves in compared samples. In estimating variation in outline, shape and relative size of the brachiopod skeleton, very many measurement
Size: 2264px × 1104px
Photo credit: © Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauthorbritishmuseumnaturalhistory, bookcentury1900, bookcoll
