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Size and shape variations in populations of 3 species of recent brachiopods have been analyzed statistically. Samples of 2 of the species, Magellania venosa (Solander) and Terebratella dorsata (Gmelin), were collected in the Strait of Magellan at depths ranging from 6–300 m and along the continental slope to a depth of 900 m. Neorhynchia strebeli (Dall) is an abyssal species, collected in the South Pacific Ocean south of the Chile Rise. Comparison of growth patterns between M. venosa and T. dorsata shows that the relative growth-ratio of width to length is identical in both species, size increase tending to follow a slightly curvilinear growth trend. The thickness-length relation differs somewhat in the 2 species. Correlation coefficients determined from pooled sample data for each species are 0.99 for width-length and 0.98 for thickness-length. Frequency distributions of length illustrate graphically the strong influence of environment on size of individuals. Histograms of samples of T. dorsata and M. venosa from the red algal zone immediately below the low tide zone are positively skewed, with means of less than 10 mm. Histograms of samples obtained from environments where the substrate is rocky or shell-covered and devoid of silt had a polymodal distribution with means more than twice those in the algal zone. The polymodal histogram for M. venosa suggests that this species is a seasonal breeder, while the normally distributed sample of N. strebeli indicates that this species breeds throughout the year. Size increase or growth trend of the variables length, width, and thickness is considered to be represented by the first principal component. It is possible to consider the shape variation between the three variables as the second and third principal components. A scatter diagram of the latter has been plotted for 3 samples of M. venosa to study the shape variation between the sampled populations. A frequency distribution of these factors has been constructed to further accent this variation. Although the samples overlap, a separation is still apparent. The analysis discloses that the character most influenced by environment is size. Over 99% of the variation in samples of M. venosa is attributed to size as determined by multivariate analysis. But this fact is also apparent when the means and frequency distributions are compared between samples from a marginal environment where there is a high mortality rate of young and a favorable environment where the populations can reach adulthood. Shape variation in M. venosa, although small, is significant in the 3 sampled populations.