Intraspecific variation in the echinoid genus Dendraster is studied by means of a statistical analysis of variation in the living species: D. excentricus. The character is analyzed in samples from 34 collections of D. excentricus. This character is prominent in current classifications of the genus. It is found that observed eccentricity data are biased by an allometric relation between eccentricity and test length. This allometry is described by an empirically derived curve. The parabolic function defining this allometric curve is used to eliminate the length bias from the eccentricity data. No systematic geographic variation is recognized in D. excentricus as reflected in the character eccentricity. However, the species may be divided into two ecological races on the basis of eccentricity. The race inhabiting sheltered bays is significantly less eccentric than the race living along the open coast. The eccentricity data for D. excentricus are employed in a review of the classification of the fossil members of the genus. The heretofore unrecognized allometry and ecological variation in Dendraster may explain some of the difficulties encountered in the fossil classification. It is found that there are greater differences in eccentricity between populations of D. excentricus than there are between species in the fossil record.
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