In the last few years the exceptionally large monothalamous arenaceous rhizopod,Astrorhiza limicola Sandahl, 1858, has been collected in appreciable numbers from the Blythand Plymouth areas of British coastal waters. These collections of the living animals have enabled the authors, both independently and jointly, to make certain observations of the behaviour of the animal, and of the structure of the test, which have not been appreciated hitherto. With the exception of two early accountsof A.limicola, one by Bessels (1875) under the name Haeckelina gigantea and the other by Schultz (1915), very little appears to be known of the biology ofany member of the family Astrorhizidae.