From a three square meter plot of intertidal shore on a rocky point of York, Maine, sea urchins (Strongylocentrotus droebachiensis) were collected on June 28 and 29, 1957 for study of their size-frequency distribution. Test height, test weight, number of wedges in the spines, number of pore-pairs in the ambulacral arcs, number of ocular plates insert, and number of coronal plates have been related to test diameter....