_Hyopotamus_, _Dichobune_, _Xiphodon_, and _Cainotherium_ were four-toed Upper Eocene transitional forms approaching the Ruminants, but all possessing upper cutting-teeth, the last-named differing but little from the Deerlets. _Oreodon_ is a genus of small pig-like animals, appearing first in the Miocene of North America, and evidently closely related to the Ruminantia. _Sivatherium_ was a gigantic Ruminant with four horns in pairs, and evidently a trunk. Its remains are found in the Miocene deposits of the Sewalik hills of India. Deer, Oxen, Goats, and Sheep first appeared in the Pliocene period, as did Camels and Llamas. Antelopes and Giraffes existed earlier, namely, in the Late Miocene. It is a fact of interest that Camels are abundant in the Miocene and Pliocene of North America, whilst they are only very scantily distributed in the same strata of the Old World, Arabia and Asia being their sole living habitat. Among the most interesting of the Pleistocene species which has been discovered in Great Britain is the gigantic Irish deer, a species originally included with the Elk, on account of the palmation and outward inclination of its huge antlers, in some specimens only a few inches less than eleven feet in span, and each more than five feet long in a straight line from burr to tip. In general form the antlers do not strikingly differ from those of the Common Fallow Deer. The brow-tyne is quite simple at its base, and generally slightly bifid at its extremity, there being no true “bez.” The beam is cylindroid as far as the insignificant “trez,” beyond which it is flattened out into a gigantic triangular expansion, or “palm,” with the free base developed into snags, usually about seven in number, and a fairly independent posterior tyne. [Illustration: IRISH ELK. (_Restored._)] At the withers the skeleton, which is quite cervine in every detail, measures as much as six feet; its great peculiarity in the male being the large size of the cervical or neck vertebræ, necessarily extra strong that they may support the massive antlers, about seventy pounds in weight. In the females, which had no cranial appendages, the vertebræ of the neck were one-third smaller. The accompanying figure is an attempt to represent the species under consideration, as it must have appeared when living. It is worthy of note, however, that as the coat of the Fallow Deer, which may be its nearest ally, is brilliantly spotted, the great Irish Deer may have resembled it in that respect. The first fairly complete skeleton of the species was found in the Isle of Man. Others have been obtained from Waterford and elsewhere in Ireland. A. H. GARROD. [Illustration: PRAIRIE DOG.] ORDER RODENTIA. CHAPTER I. INTRODUCTION--THE SQUIRREL, MARMOT, ANOMALURE, HAPLODONT, AND BEAVER FAMILIES.