Some Observations on the Growth Rate of Sea Urchins in the Genus Strongylocentrotus

For certain areas of the New Hampshire and southern Maine coasts, evidence has been accumulating indicating that in June of the year of settling S. drocbachiensis have attained a size of only ½—1½ mm. in test diameter, and that the modes of subsequent year classes are approximately 8-l0, 24-26, 40-42 and somewhere between 46 and 54 mm. 2. S. droebachiensis was found to grow considerably faster in test cages at Friday Harbor, Washington, but differences in the food supplied might be responsible, at least in part, for this difference. 3. Exploratory tests on growth rate were carried out at Friday Harbor on S. echinoides, S. purpuratus, and S. franciscanus. 4. Observations of earlier workers on growth rate in sea urchins of the genus Strongylocentrotus have been reviewed and compared with the present findings.