Our fossil lamantins differ from those known to exist at present, in having the head more elongated, and of a different form[266]. Their ribs, which are easily recognised by their being of a thick and rounded form, and of dense texture, are not of rare occurrence in our different provinces. With regard to the fossil morse, small fragments only have as yet been found of it, which are insufficient for characterising the species[267]. It is only in the strata that have succeeded the coarse limestone, or, at most, those which may have been of contemporaneous formation with it, but deposited in fresh-water lakes, that the class of land mammifera begins to shew itself in any quantity. I consider as belonging to the same period, and as having lived together, but perhaps in different spots, the animals whose bones are deposited in the molasse and old gravel beds of the south of France; in the gypsums mixed with limestone, such as those of Paris and Aix; and in the fresh-water marly deposits covered with marine beds, of Alsace, the country of Orleans and of Berry. This animal population possesses a very remarkable character in the abundance and variety of certain genera of pachydermata, which are entirely awanting among the quadrupeds of our days, and whose characters have more or less resemblance to those of the tapirs, the rhinoceroses, and camels. These genera, the entire discovery of which is my own, are the _palæotheria_, _lophiodonta_, _anaplotheria_, _anthracotheria_, _cheropotami_, and _adapis_. The _Palæotheria_ have resembled the tapirs in their general form, and in that of the head, particularly in the shortness of the bones of the nose, which announces that they have had a small proboscis like the tapirs, and, lastly, in their having six incisors and two canine teeth in each jaw; but they have resembled the rhinoceros in their grinders, of which those of the upper jaw have been square, with prominent ridges of various configuration, and those of the lower jaw in the form of double crescents, as well as in their feet, all of which have been divided into three toes, while in the tapirs the fore feet have four. It is one of the most extensively diffused genera and most numerous in species that occur in the deposits of this period.