DEVONIAN AND OLD RED PERIOD. 139 
as probably the spore-cases of the minute plants known as 
Desmidie. 
A Pas 
X (i —~s2 
fr 
—, 
a 
i ~ Ses 
\ = ys 
Fig. 78.—A, Trunk of Prototaxites Loganz, eighteen inches in diameter, as seen in the 
cliff near L’Anse Brehaut, Gaspé; B, Two wood-cells showing spiral fibres and obscure 
pores, highly magnified. Lower Devonian, Canada. (After Dawson.) 
The Devonian Profozoans have still to be fully investigat- 
ed. True Sponges (such as Astreospongia, Spherospongia, 
&c.) are not unknown; but by far the commonest repre- 
sentatives of this sub-kingdom in the Devonian strata are 
Stromatopora and its allies. These singular organisms (fig. 
79) are not only very abundant in some of the Devonian lime- 
stones—both in the Old World and the New—but they often 
attain very large dimensions. However much they may differ 
in minor details, the general structure of these bodies is that 
of numerous, concentrically-arranged, thin, calcareous lamine, 
separated by narrow interspaces, which in turn are crossed by 
numerous delicate vertical pillars, giving the whole mass a 
cellular structure, and dividing it into innumerable minute 
quadrangular compartments. Many of the Devonian Stvomato- 
pore also exhibit on their surface the rounded openings of 
canals, which can hardly have served any other purpose than 
that of permitting the sea-water to gain ready access to every 
part of the organism. 
No true Graptolites have ever been detected in strata of 
