t under
the name of _Eopkyton_ (fig. 28). It cannot be said, however,
that the vegetable origin of these singular bodies has been
satisfactorily proved. Lastly, there are found in certain green
and purple beds of Lower Cambrian age at Bray Head, Wicklow,
Ireland, some very remarkable fossils, which are well known under
the name of _Oldhamia_, but the true nature of which is very
doubtful. The commonest form of _Oldhamia_ (fig. 29) consists of
a thread-like stem or axis, from which spring at regular intervals
bundles of short filamentous branches in a fan-like manner. In
the locality where it occurs, the fronds of _Oldhamia_ are very
abundant, and are spread over the surfaces of the strata in tangled
layers. That it is organic is certain, and that it is a calcareous
sea-weed is probable; but it may possibly belong to the sea-mosses
(_Polyzoa_), or to the sea-firs (_Sertularians_).

Amongst the lower forms of animal life (_Protozoa_), we find the
Sponges represented by the curious bodies, composed of netted
fibres, to which the name of _Protospongia_ has been given (fig.
32, a); and the comparatively gigantic, conical, or cylindrical
fossils termed _Archoeocyathus_ by Mr Billings are certainly
referable either to the _Foraminifera_ or to the Sponges. The
almost total absence of limestones in the formation may be regarded
as a sufficient explanation of the fact that the _Foraminifera_
are not more largely and unequivocally represented; though the
existence of greensands in the Cambrian beds of Wisconsin and
Tennessee may be taken as an indication that this class of animals
was by no means wholly wanting. The same fact may explain the
total absence of corals, so far as at present known.

[Illustration: Fig. 29.--A portion of _Oldhamia antiqua_, Lower
Cambrian, Wicklow, Ireland, of the natural size. (After Salter.)]

The group of the _Echinodermata_ (Sea-lilies, Sea-urchins, and
their allies) is represented by a few forms, which are principally
of interest as being the earliest-known examples of the class.
It is also worthy of note that these precursors of a group which
subsequently attains such geological importance, are referable to
no less than three distinct _orders_--the Crinoids or Sea-lilies,
represented by a species of _Dendrocrinus_; the Cystideans by
_Protocystites_; and the Star-fishes by _Palasterina_ and some
other forms. Only the last of these groups, however, appears
to occur in the Lower Cambrian.

[Il