In addition to the water-inhabiting group of the Crustaceans, we find the articulate animals to be represented by members belonging to the air-breathing classes of the _Arachnida, Myriapoda_, and _Insecta_. The remains of these, as might have been expected, are not known to occur in the marine limestones of the Carboniferous series, but are exclusively found in beds associated with the Coal, which have been deposited in lagoons, estuaries, or marshes, in the immediate vicinity of the land, and which actually represent an old land-surface. The _Arachnids_ are at present the oldest known of their class, and are represented both by true Spiders and Scorpions. Remains of the latter (fig. 123) have been found both in the Old and New Worlds, and indicate the existence in the Carboniferous period of Scorpions differing but very little from existing forms. The group of the _Myriapoda_, including the recent Centipedes and Galley-worms, is likewise represented in the Carboniferous strata, but by forms in many respects very unlike any that are known to exist at the present day. The most interesting of these were obtained by Principal Dawson, along with the bones of Amphibians and the shells of Land-snails, in the sediment filling the hollow trunks of _Sigillaria_, and they belong to the genera _Xylobius_ (fig. 124) and Archiulus. Lastly, the true _insects_ are represented by various forms of Beetles (_Coleoptera_), _Orthoptera_ (such as Cockroaches), and _Neuropterous_ insects resembling those which we have seen to have existed towards the close of the Devonian period. One of the most remarkable of the latter is a huge May-fly (_Haplophlebium Barnesi_, fig. 125), with netted wings attaining an expanse of fully seven inches, and therefore much exceeding any existing Ephemerid in point of size. [Illustration: Fig. 126.--Carboniferous _Polyzoa_. a, Fragment of _Polypora dendroides_, of the natural size, Ireland; a' Small portion of the same, enlarged to show the cells; b, Glauconome pulcherrima_, a fragment, of the natural size, Ireland; b', Portion of the same, enlarged; c, The central screw-like axis of _Archimedes Wortheni_, of the natural size--Carboniferous, America; c', Portion of the exterior of the frond of the same, enlarged; c'', Portion of the interior of the frond of the same showing the mouths of the cells, enlarged. (After M'Coy and Hall.)]