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BRITISH STROM ATOPOROIDS. 



is from ^ to 3- mm. in diameter, and has a peculiar porous or tubulated structure, 

 which will be more fully described hereafter, but the most characteristic feature of 

 which is the appearance, in thin sections, of isolated clear spaces of comparatively 

 considerable size within the substance of the fibre (Plate XXV, figs. 4 — 7). The 

 skeleton-fibre thus constituted is woven into an irregular network enclosing the 

 vertical, straight or flexuous zooidal tubes. In tangential sections (Plate XXV, 

 fig. 4) this irregular reticulation is seen to be traversed by the scattered and com- 

 monly tabulate branches of the astrorhizse, and pierced by the variably shaped aper- 

 tures of the transversely divided zooidal tubes. Vertical sections (Plate XXV, 

 figs. 5 and 9) show that the ccenosteal tissue is composed of thick and irregular 

 radial pillars united at intervals by thick horizontal or oblique connecting-pro- 

 cesses, the network thus formed enclosing numerous zooidal tubes, which are 

 furnished with well-developed transverse tabulae. About six zooidal tubes, with 

 their intervening pillars, occupy a space of 2 mm. measured transversely. 



Obs. — The coenosteum of P. Ooldfussii, Barg., is typically spheroidal, pyriform, 

 or clavate in shape (woodcut, Fig. 22), and is usually of small size. The 



Fig. 22. 



Pig. 22. — A small specimen of Parallelopora Goldfussii, Barg., from the Middle Devonian 

 of Hebborn, viewed sideways ; of the natural size. 



specimens from the Middle Devonian Rocks of Hebborn (Paffrath district) are 

 mostly stunted, being usually about 2 to 3 cm. in diameter ; whereas those 

 from Steinbreche near Refrath, in the same area, are of considerably larger size. 

 There is no trace of an epitheca in such specimens as I have seen ; and the 

 coenosteum often envelops corals and other foreign bodies. The specimens from 

 Devonshire, being mostly derived from the Devonian pebbles in the Triassic 

 breccias of that region, have no recognisable form as a rule ; but a badly preserved 

 example from Dartington, apparently referable to this species, has a massive 

 coenosteum of considerable size, with much-undulated laminae. 



The astrorhizal system is remarkably variable in its development in this 

 species. Some examples show only very small and scattered astrorhizse ; but the 

 typical state of things is to find irregularly distributed astrorhizse consisting of 

 a few slightly branched canals of large size, the internal cavities of these being 



