To the Geological Society, on the other hand, of which he became a Fellow in the year 1886, Sir William contributed three papers on paleontological subjects, by far the most important of which was one on the affinities and probable habits of the extinct Australian marsupial _Thylacoleo_. Further allusion to this is made in the sequel. Of the other two, one recorded the occurrence of teeth of the bear-like _Hyænarctus_ in the Red Crag of Suffolk, and the other that of a skull of the manatee-like _Halitherium_ in the same formation. Of the Anthropological Institute of Great Britain and Ireland Flower was elected a Vice-President in 1879, while in 1883 he succeeded to the Presidential chair, and occupied that position till 1885. Of his numerous contributions to anthropological science, many appeared in the journal of the Institute. In the annual meetings of the British Association for the advancement of science, Flower, from an early date, took a lively interest. At the Norwich meeting, in 1868, he acted as Vice-President of the section of Biology, while he was President of the same section at the Dublin meeting of 1878. At York he presided over the section of Anthropology in 1881; he was a Vice-President at the Aberdeen meeting of 1885, while for the second time he occupied the Presidential chair of the Anthropological section in 1894 at Oxford, when his opening address on Anthropological progress displayed great breadth of thought and generalisation. Finally, he was President of the Association at the meeting held in Newcastle-on-Tyne in 1889, his address at the latter meeting forming the first article in _Essays on Museums_.