DEVONIAN AND OLD RED PERIOD. 



139 



as probably the spore-cases of the minute plants known as 

 DesjTiidicB. 



Fig 78. — A, I'runk o{ Prototaxitcs Lognni, eighteen inches in diameter, as seen in the 

 cliff near L'Anse Brehaut, Gaspe ; B, Two wood-cells showing spiral fibres and obscure 

 pores, highly magnified. Lower Devonian, Canada. (After Dawson.) 



The Devonian Protozoans have still to be fully investigat- 

 ed. True Sponges (such as AstrcEospongia, Sphcerospongia, 

 &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 Hme- 

 stones — both in the Old ^Vorld 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 laminae, 

 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 Stromato- 

 porce 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 



