At what date Flower first began to study whales seriously, it is not easy to ascertain. From the fact of his contributing three papers on this subject to the Zoological Society’s _Proceedings_ for 1864, it may, however, be inferred that by that time he had devoted no inconsiderable amount of attention to the group. In the first of those he described a specimen of a lesser fin-whale, then recently stranded on the Norfolk coast; while in a second, and much more important communication, he gave notes on the skeletons of whales preserved in the museums of Holland and Belgium which he had recently visited. Two of these he described as indicating apparently new species; although their right to distinction was not maintained. In the same year he described two skulls of grampuses from Tasmania, which were regarded as representing a new species, under the name of _Orca meridionalis_; a further note on these being added in the Society’s _Proceedings_ for 1865, when the species was transferred to the genus _Pseudorca_. Later still it was found that the supposed species was inseparable from the typical _P. crassidens_; named by Owen many years previously on the evidence of a skeleton from the Lincolnshire Fens. In another note published the same year in the same journal he showed that one of the whales named by him in 1864 was identical with the one now known as _Balænoptera sibbaldi_; while a second paper described a specimen of the fin-whale commonly known as _B. musculus_. A further note on the synonymy of _B. sibbaldi_ appeared in the _Proceedings_ for 1868. Reverting to earlier publications, in 1866 the Royal Society of London issued a volume containing translations by Flower of certain very important memoirs on Cetacea by Professors Eschricht, Reinhardt, and Lilljeborg. As these were written in a language understood by comparatively few Englishmen, the translation was a distinct benefit to “cetology” in this country. Between the years 1869 and 1878 inclusive, six very important memoirs on whales (including in that term porpoises, dolphins, etc.) from Flower’s pen appeared in the _Transactions_ of the Zoological Society of London. The first of these, which was published in the year first mentioned, was devoted to the description of the skeleton of the very interesting and then little-known South American freshwater or estuarine dolphins, _Inia_ and _Pontoporia_. In the course of this memoir it was demonstrated that, in spite of the wide distance between their habitats, these dolphins and the freshwater dolphin of the Ganges and certain other Indian rivers, _Platanista gangetica_, collectively form a distinct family group—the Platanistidæ, which exhibits many very generalised features.