THE CAMBRIAN PERIOD. SI 
beds of Lower Cambrian age at Bray Head, Wicklow, Ireland, 
some very remarkable fossils, which are well known under the 
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Fig. 28.—Fragment of Zophyton Linneanumt, a supposed land-plant, Lower 
Cambrian, Sweden, of the natural size. 
name of O/dhamia, but the true nature of which is very doubtful. 
The commonest form of O/dhamia (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 O/dhamua 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 (/olyzoa), or to the sea-firs (Sertudarians). 
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 cylin- 
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