he 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.)]

The lower groups of the _Mollusca_ are abundantly represented
in the marine strata of the Carboniferous series by _Polyzoans_
and _Brachiopods_. Amongst the former, although a variety of other
types are known, the majority still belong to the old group of
the "Lace-corals" (_Fenestellidoe_), some of the characteristic
forms of which are here figured (fig. 126). The graceful netted
fronds of _Fenestella, Retepora_, and _Polypora_ (fig. 126, a)
are highly characteristic, as are the slender toothed branches
of _Glauconome_ (fig. 126, b). A more singular fo