A new species of Proterythropsis is described; P. vigilans. Diagnosis: a small ovoidal form, length 1.4 times the greatest width ; girdle a descending left spiral of one and a quarter turns, with a continuation on to the tentacle ; sulcus describing nearly half a turn. Ocellus of compact type, posterior ; lens pear-shaped ; red pigment-mass with reddish yellow core. Slender tentacular process carrying continuation of girdle. Compound capsules present, each containing six smaller capsules. It occurred at Millport in March and April, 1928 and 1924.