There is a fourth species still (_Rh. minutus_), furnished, like the second, with incisors, but of a much smaller size, and scarcely larger than a hog[307]. It was undoubtedly rare, for the remains of it have only as yet been found in some places in France. To those four genera of large pachydermata, is added a Tapir, which equalled them in size, and was consequently twice, perhaps three times, as large in its linear dimensions as the American Tapir[308]. Its teeth have been found in several parts of France and Germany; and almost always accompanying those of rhinoceroses, mastodons, or elephants. Along with these there is still associated, but as it would seem in a very small number of places, a large pachydermatous animal, of which the lower jaw alone has been found, and whose teeth are of the form of double crescents, and undulated. M. Fischer, who discovered it among bones from Siberia, has named it _Elasmotherium_[309]. The Horse genus also existed in those times[310]. Its teeth accompany in thousands the remains of the animals which we have just mentioned, in almost all their localities; but it is not possible to say whether it was one of the species now existing or not, because the skeletons of these species are so like each other, that they cannot be distinguished by the mere comparison of isolated fragments. The Ruminantia were now greatly more numerous than at the epoch of the Palæotheria; their numerical proportion must even have differed very little from what it is at present; but we are certain of several species which were different. This may, in particular, be said with much certainty of a deer exceeding even the elk in size, which is common in the marl deposits and peat-bogs of Ireland and England, and of which remains have also been dug up in France, Germany, and Italy, where they were found in the same strata with bones of elephants. Its wide, palmated, and branched horns, measure so much as twelve or fourteen feet from one point to the other, following the curvatures[311]. The distinction is not so clear with regard to the bones of deer and oxen, which have been collected in certain caverns, and in the fissures of certain rocks. They are sometimes, and especially in the caverns of England, accompanied with bones of elephants, rhinoceroses, and hippopotami, and with those of a hyena, which also occurs in several strata of transported matter, along with these same pachydermata. They are consequently of the same age; but it remains not the less difficult to say in what respect they differ from the oxen and deer of the present day.