The two remaining memoirs in the _Transactions_, which appeared respectively in 1873 and 1878, were devoted to that difficult, and at the time imperfectly known group, termed ziphioid, or beaked whales. In the first of the two attention was concentrated on the aberrant and rare form known as _Berardius arnuxi_; while the second was exclusively devoted to the much more abundant types included under the generic title _Mesoplodon_, in allusion to the single pair of lower teeth near the middle of the sides of the lower jaw, which forms the single dental armature of the cetaceans of this genus. The beaked whales, it should be added, had been previously discussed by Flower in a preliminary paper published in the Zoological Society’s _Proceedings_ for 1871 and 1876, and likewise in an article communicated in 1872 to _Nature_. Special interest attaches to a paper by Flower published in the _Transactions_ of the Royal Geological Society of Cornwall for 1872, and also in the _Annals and Magazine of Natural History_ for the same year, on the bones of a whale dug up at Petuan, in Cornwall, sometime previously to 1829, and now preserved in the museum of the above-named Society. The whale represented by these remains was made the type of the new genus and species _Eschrichtius robustus_, by the late Dr. J. E. Gray. That it was a member of the group of whalebone-whales, and that it could not be identified with either of the genera then known, namely _Balæna_, _Balænoptera_, and _Megaptera_, was fully demonstrated by Flower, who also showed that it agreed with the two latter in having the neck-vertebræ free. “The interesting question,” he added, “remains, whether this species still exists in our seas; if extinct, it must have become so at a comparatively recent period, certainly long after Cornwall was inhabited by man. The negative evidence of no specimen having been met with by naturalists in a living or recent state, is hardly conclusive as to its non-existence, as our knowledge of this group of animals is lamentably deficient. We are acquainted with many species, even of very large size, only through isolated individuals, and the discovery of others new to science is by no means an infrequent or unlooked-for occurrence at the present time.” In the opinion of the present writer, it is quite probable that this whale may be identical with the grey whale of the Pacific, described many years subsequently by the late Professor Cope as _Rhachianectes glaucus_, in which event that name will have to give place to _Eschrichtius robustus_.