Abstract
The nematode Halenchus fucicola (de Man), causing galls on the thallus of the sea weed yAscophyllum nodosum, has been found in the Plymouth area (Wembury Bay) and at Croyde Bay on the north Devon coast, and a redescription of the worm is given. A new species of Halenchus (H. dumnonicus) causing similar growths on the sea weeds Fucus vesiculosus and F. serratus is described. This latter form is also found at Wembury Bay; at Looe, Cornwall, and at Lyme Regis, Dorset.