Finally, the Crustaceans include the genera _Pagurus_ (or the Hermit crabs); _Astacus_. (the lobster); and _Portunus_ (or paddling crabs). Of the first, it is doubtful if any fossil species have been found; of the last, species have been discovered bearing some resemblance to _Podophthalmus vigil_, as _P. Defrancii_, which only differs from it in the absence of the sharp spines which terminate the lateral angles of the carapace in the former; while _Portunus leucodon_ (Desmarest) bears some analogy to Lupea. [Illustration: XXIV.--Ideal Landscape of the Miocene Period.] * * * * * [Illustration: Fig. 171.--Podophthalmus vigil.] An ideal landscape of the Miocene period, which is given on the opposite page (PLATE XXIV.), represents the Dinotherium lying in the marshy grass, the Rhinoceros, the Mastodon, and an Ape of great size, the _Dryopithecus_, hanging from the branches of a tree. The products of the vegetable kingdom are, for the greater part, analogous to those of the present time. They are remarkable for their abundance, and for their graceful and serried vegetation; and still remind us in some respects, of the vegetation of the Carboniferous period. It is, in fact, a continuation of the characteristics of that period, and from the same cause, namely, the submersion of land under marshy waters, which has given birth to a sort of coal which is often found in the Miocene formation, and which we call _lignite_. This imperfect coal does not quite resemble that of the Carboniferous, or true Coal-measure period, because it is of much more recent date, and because it has not been subjected to the same internal heat, accompanied by the same pressure of superincumbent strata, which produced the older coal-beds of the Primary epoch. [Illustration: Fig. 172.--Lupea pelagica.] The _lignites_, which we find in the Miocene, as in the Eocene period, constitute, however, a combustible which is worked and utilised in many countries, especially in Germany, where it is made in many places to serve in place of coal. These beds sometimes attain a thickness of above twenty yards, but in the environs of Paris they form beds of a few inches only, which alternate with clays and sands. We cannot doubt that lignites, like true coal, are the remains of the buried forests of an ancient world; in fact, the substance of the woods of our forests, often in a state perfectly recognisable, is frequently found in the lignite beds; and the studies of modern botanists have demonstrated, that the species of which the lignites are formed, belong to a vegetation closely resembling that of Europe in the present day.