REVIEWING the recently published “Introduction to the Study of Mammals” by Prof. Flower and Mr. Lydekker, Prof. Lankester states (suprà, p. 122) that “The authors of the present work mention Dr. Heilprin's opinion that the Palæarctic and Nearctic regions should be united and called the Holarctic region. But they do not adopt this opinion, nor refer to Huxley's proposal to term this same area Arctogæa,” and so on. Now, in this last statement my good friend the reviewer, perhaps writing from memory, is mistaken. Had Prof. Huxley proposed to limit his “Arctogtæa” to the Palæarctic and Nearctic regions of Mr. Sclater and Mr. Wallace, I should certainly not have suggested to Prof. Heilprin a new name for that combination. Anyone looking to the passage (Proc. Zool. Soc., 1868, pp. 314, 315) in which Prof. Huxley defined his “Arctogæa”—a name to which, let me say, I have not the least objection—will see that it signifies that part of the world which is not “Notogæa,” and therefore includes the Ethiopian and Indian regions of Mr. Sclater, whereas my “Holarctic” region expressly excludes them, and is therefore a very different thing from “Arctogæa” in its true sense.