In the year 1879, and for some time after, Flower directed his attention more especially to the dolphins and porpoises, which collectively constitute the family Delphinidæ of naturalists, and he published a series of papers on this group in the _Proceedings_ of the Zoological Society. In the volume for 1879 there appeared, for instance, one paper on the common dolphin (_Delphinus delphis_); a second on the bottle-nosed dolphin, now known as _Tursiops tursio_; and a third on the skull of the white whale, or beluga (_Delphinapterus leucas_). Of far greater importance was, however, the appearance in 1883 of a paper in the same serial on the generic characters of the family Delphinidæ as a whole. Special attention was directed in this communication to the value of the pterygoid bones, on the under surface of the skull, in the classification of the family; and characters were formulated which enabled the various genera to be identified, wholly or in part, by this part of the skull. Flower’s classification of the Delphinidæ has, with some slight modifications, been very generally accepted by later naturalists. Some time after the publication of this paper the present writer pointed out to the author that two of the generic names employed by him were barred by previous use in a different sense; and in a note subsequently published in the _Proceedings_, these were accordingly replaced. Flower was, however, by no means forgetful of his earlier love for the cachalot and beaked whales (Physeteridæ); and in 1883 and again in 1884 he published papers in the _Proceedings_ on their near relatives the bottle-nosed whales (not to be confounded with the bottle-nosed dolphins) of the genus _Hyperöodon_. In these investigations he was much indebted, as on several previous occasions, to the observations of Captain Gray, a well-known whaler. As regards the common bottle-nose (_H. rostratus_), Sir William succeeded in demonstrating that the great differences which had long been noticed in the skull were due to distinctions either of sex or age; the old males developing huge maxillary crests—with a broad and flattened front surface—of which there is scarcely any trace in the younger members of the same sex, or in females of all ages. In consequence of this difference in the skull, the head of the old bull bottle-nose is easily recognisable by the abrupt and prominent elevation of the forehead immediately behind the base of the beak. Flower was also able to show that bottle-noses yield true spermaceti, especially in the head; a fact which does not appear to have been previously known to zoologists, although it may have been to whalers. At the present day there is a considerable trade in bottle-nose sperm-oil and spermaceti; these being often blended with the products of the cachalot, from which they are distinguishable by their specific gravity. In his 1882 paper Flower described a water-worn bottle-nose skull from Australia, which