GENUS IDIOSTROMA. 



101 



pillars thoroughly recognisable as distinct structures, but the concentric laminae 

 are conspicuous in both transverse and longitudinal sections of the stem. Trans- 

 verse sections of the stems also show very clearly, as also longitudinal ones do less 

 perfectly, that the entire ccenosteum is traversed by innumerable distinct zooidal 

 tubes, which radiate outwards from the axis of the stems to open on the surface by 

 distinct apertures, and which are crossed by numerous curved or straight tabulas 

 (Plate IX, fig. 8). Lastly, thin sections show that the skeleton-fibre has the 

 minutely porous character which is such a marked feature in the case of the species 

 of Stromatopora, Goldf. 



A second still more remarkable species of Idiostroma occurs in the Devonian 

 Rocks of Britain and Germany, which may be provisionally distinguished by the 

 name of J. oculatum. I was under the impression that this would prove to be identical 

 with the fossil described and figured by Kayser from the Devonian Rocks of the 

 Eifel under the name of Trachypora circulvpora (' Zeitschr. der deutschen Geol. 

 Gesell.,' 1879, p. 304, Taf. v, figs 2 — 4), with which it agrees closely in aspect 

 and general appearance. Professor Schliiter, however, having examined the 

 original specimens of Trachypora circulvpora, Kays., informs me that though the 

 fossil so named may be in part of the nature of a Stromatoporoid, it is not the 

 same as the singular dendroid Idiostroma here in question. I have therefore 

 thought it best to distinguish the latter by the above-mentioned title. 



The ccenosteum in Idiostroma oculatum (Fig. 14) consists of slender cylindrical 

 stems, from three to five mm. in diameter, which branch and inosculate freely, so 



P10. 14. 



Fig. 14. — A fragment of the ccenosteum of Idiostroma oculatum, n. sp., of the natural size. 

 Devonian, Biichel. a. A small portion of the surface enlarged 



as to give rise to large fasciculate masses. The general structure of the skeleton 

 is essentially the same as in the previously described I. Roemeri. Each cylindrical 

 stem is traversed by a large axial canal, which is intersected by transverse, curved, 



14 



