GENUS IDIOSTROMA. 99 



Idiostroma, but can be readily distinguished from all the other members of this 

 group by the peculiar minute tabulation of the skeleton-fibre. Lastly, Amphipora, 

 Schulz, in the complete reticulation of its skeletal tissue, and in the apparently 

 compact character of its skeleton-fibre, stands quite alone ; though it agrees with 

 the cylindrical forms of Idiostroma and Staehyodes in the shape of the coenosteum, 

 and in the very striking character that it possesses a principal axial tabulate tube. 

 I should, however, be inclined to think that Amphipora might perhaps be regarded 

 as the type of a separate group. 



Genus Idiostroma, Winchell. 



(' Proc. Artier. Assoc. Adv. of Science,' p. 99, 1867.) 



The coenosteum is typically cylindrical, sometimes fasciculate, sometimes 

 massive or sub-massive. The general skeletal tissue is reticulated, but the radial 

 pillars and concentric laminae remain largely distinct from one another. The 

 skeleton-fibre is coarsely porous. Definite zodidal tubes, furnished with numerous 

 tabular, and opening on the surface by rounded apertures, are present. In addition 

 to the ordinary zooidal tubes there are present larger tabulate tubes. In typical 

 examples of the genus each cylinder of the skeleton has a single tabulate axial tube, 

 which gives off secondary lateral tubes, also intersected by tabula?. In the massive 

 and sub-massive examples the large tubes are irregularly distributed through the 

 mass. These tubes may be only bounded by the general tissue of the skeleton, or 

 they may be enclosed by definite walls, which may be thickened towards their 

 mouths. In any case the tubes communicate more or less extensively with the 

 interlaminar spaces. The surface shows prominent pointed tubercles, often 

 arranged in vermiculate ridges, which may radiate from prominent conical 

 "mamelons," so as to form imperfect astrorhizae. The openings of the small 

 zooidal tubes are placed in the grooves separating these vermiculate ridges. The 

 conical " mamelons " may or may not have large apertures at their summits. 



The genus Idiostroma was founded by "Winchell for the reception of two species 

 {I. ccespitosum and I. gordiaceum) from the Devonian Rocks of North America. 

 I. cwspitosum has subsequently been described and figured, presumably from 

 American specimens, by Quenstedt, under the name of Stromatopora cmspitosa 

 (' Die Schwamme,' pi. 142, fig. 14, 1878). My own knowledge of the genus is 

 based upon a large series of specimens belonging to three different species, of 

 which two are common to the Devonian Rocks of Germany and of Devonshire, 



