The athyrid genus Composita ranges from Late Devonian or Early Pennsylvanian to Permian (Guadalupe) in North America; 42 American species and varieties are included in a phylogenetic history, nine species are listed as doubtful, and 18 names are rejected. Five common associated species from five localities in the Pennsylvanian and Permian of Illinois and Kansas are studied quantitatively. Frequency polygons, triangular graphs, and reduced major axis comparison are used to determine relations of the species in the five collections. C. subtilita, C. argentea, C. ovata, C. magma, and C. elongata are now regarded as typological species; C. subtilita, the most abundant and ubiquitous, intergrades with all the others, but they do not intergrade with each other.

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