Styela mammiculata n.sp. is based on four specimens collected in the Plymouth area during the summer of 1953. The most noticeable external feature is the extensive mammillation of the test. The mammillae are much smaller than those of Phallusia mammillata and deserve to be called rather ‘mammiculae’.Of the four specimens, two were taken from Drake's Island buoy (National Grid Reference, 20/4753)m Plymouth Sound, growing about half a metre below the water line, and two from the oyster bed of the Lynher river estuary, near Antony Ferry (National Grid Reference, 20/4257), growing about 12 m. below low-tide mark attached to oyster shells. The largest specimen was from the latter locality and measured III mm. long in the contracted, fixed condi- tion. The smallest, from Drake's Island buoy, was 54 mm. long.