Controversy concerning the affinity of the stromatoporoids is not new; it began over 100 years ago with the first systematic studies of the group. Rosen's (1867) opinion was that these fossils were allied to the sponges. Nicholson and Murie (1878) agreed. Solomko (1885) introduced some of the arguments still used by the advocates of the poriferan affinity of the stromatoporoids such as the recognition of the astrorhizae as excurrent canal systems. H.A. Nicholson who had at first supported the hypothesis of sponge affinity became convinced that the closest living representatives were to be found in the hydrozoans. He compared the skeletons of the stromatoporoids like Actinostroma to the modern hydrozoan Hydractinia and the skeleton of amalgamate genera like Stromatopora to that of Millepora. Nicholson's monograph of British stromatoporoids (1886–92) and the papers he published in the Annals and Magazine of Natural History to accompany his revision of the group form the basis of all later work and hence his views on the affinity of stromatoporoids had immense influence.