INTRODUCTION Verrill (1879: 199-200) described two specimens of Alcyonium collected on the Fishing Bank, east of Cape Cod, Massachusetts, in 80 fathoms. According to him "they form low, thick, lobular masses", "the base is somewhat spreading" and "the division into rounded or flattened lobes takes place close to the base". He is of opinion that "if not identical with A. digitatum of Europe, it is at least very closely related". More than forty years later Verrill (1922: 20) returns to this question. This time he gives a drawing of one of these American colonies (his textfigure 3), and he has changed his mind regarding the relation to A. digitatum. He now thinks the species is "distinct from the common European species, A. digitatum, to which it is nearly allied". He named it A. siderium. It is a pity that Verrill omitted an exact study of the spicules and of other characters. Deichmann (1936: 48-49) described the species more fully on the basis of "twenty-five specimens from nine localities off the coast of New England at depths varying from 8-80 fms". But she also failed to give drawings of the spicules. She found that the differences between Verrill's A. siderium and Linné's A. digitatum were insignificant, and she therefore abandoned the name siderium. Recently Dr. Arthur G. Humes, Boston University, Massachusetts, sent to me three Alcyonium colonies collected by him in the same locality as Verrill's type specimens. A hasty survey of them led me to doubt the correctness of Deichmann's conclusion, and a closer examination and comparison of both species seemed necessary to me.