HERMATOSTROMA EPISCOPALE. 219 



between the members of this series, on the view here expressed, may be 

 summarised as follows : 



1. Stromatopora. — Skeleton-fibre minutely porous ; radial pillars and their 

 connecting processes more or less indistinguishably fused to form a reticulate 

 skeleton. 



2. Stromatoporella. — The skeleton-fibre minutely porous ; the skeleton network 

 incompletely reticulate, and the radial pillars more or less clearly recognisable as 

 distinct structures. 



3. ParalMopora. — Skeleton-fibre porous and minutely canaliculated ; the 

 skeleton incompletely reticulate, and the radial pillars more or less clearly 

 recognisable, but never traversed by large axial canals. 



4. Hermatostroma. — Skeleton-fibre with large and conspicuous canaliculi, and 

 sometimes also minutely porous ; the skeleton reticulate, but showing exceedingly 

 well developed, " continuous " radial pillars, which are traversed by large axial 

 canals. 



From Hermatostroma episcopale, Nich., the only other species of the genus at 

 present known to me, the present form is at once distinguished by the greater 

 coarseness of the skeleton-fibre, the absence of astrorhizas, and the extraordinary 

 development of the canal-system of the radial pillars. 



Distribution. — Rare in the Middle Devonian Limestones of Hebborn in the 

 Paffrath district. The species has not been recognised in Britain. 



2. Hermatostroma episcopale, n. sp. PI. XXVIII, figs. 4 — 11. 



? Stbomatopoba concentrica, Phillips. Pal. Foss. of Cornwall, &c, p. 18, pi. x, 



figs. 28 a, 2SJ, 1841. 



The coenosteum in this species is massive, not composed of definite latilamina?, 

 and apparently attached at one point only ; but its mode of growth is not 

 perfectly known. It may, however, be inferred from the structure of the skeleton 

 that the surface was elevated into prominent astrorhizal eminences — " mamelons," 

 and at the same time covered with well-defined tubercles, the latter being 

 probably perforated at their apices. 



The lamina? are undulated, and well-defined "astrorhizal cylinders" are 

 developed round the astrorhizal systems (Plate XXVIII, fig. 4). The astrorhizas, 

 though of small size, are usually well developed, their centres being from 7 to 10 

 mm. apart. They are arranged in vertically superimposed systems, each system 

 having an axial wall-less canal, which doubtless opened on the surface at the apex 

 of a mamelon. 



30 



