In order to provide more factual information on the effect of Echinus predation (Forster, 1958), further diving observations have been made during 1958. A rocky areajust west of the Tinker Shoal was explored by chance and a population of Echinus discovered. As this area is much more readily accessible than Stoke Point rock, where most of the diving has been carried out, it was possible to establish a marker buoy and make a number of dives on exactly the same position. In the course of these dives I have attempted to measure the numerical density of the urchins and the rate of their browsing on the rock surface. Later Echinus ‘counts’ were made at many other positions near Plymouth (Text-fig. 1).