The Delesserias, a genus of red seaweeds, six species of which inhabit the shores of the British Isles, have the thallus differentiated into a well-marked foliar expansion and a cylindrical portion; these we may respectively term the leaf and the stalk. Descriptions of this thallus are given in all books on seaweeds, for instance, in Harvey's (Phycologia Britannica), or Hauck's (Die Meeresalgen), but as far as I am aware no detailed, account has been given of these structures.