206 BRITISH STROMATOPOROIDS. 



some specimens from the Devonian pebbles in the Triassic conglomerates of 

 Devonshire yield sections in some respects resembling those of the present species. 



3. Stromatoporella socialis, n. sp. PI. XXVI, figs. 5 — 7. 



This species is only known to me from the pebbles of Devonian Limestone in 

 the Triassic conglomerates of South Devon, and the characters of its surface and 

 its mode of growth are therefore imperfectly or not at all known. It appears, 

 however, to have been in general either laminar or massive in form, and it 

 certainly was not of an encrusting habit. The laminae of the ccenosteum are 

 always more or less extensively undulated, and sections show conclusively that 

 " astrorhizal cylinders " were usually more or less largely developed. The 

 astrorhiza?, namely, are not only well marked and of large size, but they are super- 

 imposed in vertical rows in successive lamina?, each series having a wall-less axial 

 canal round which the lamina? are concentrically wrapped (Plate XXVI, fig. 5). 

 The interspaces between the astrorhizal cylinders are occupied by undulating 

 lamina?, in the same manner as in Actinostroma verrucosum, Goldf. "We may, 

 therefore, assume that the surface, when observed, will be found to be more or 

 less extensively covered with prominent conical eminences or " mamelons," at the 

 apex of each of which the central canal of a series of astrorhiza? will open. 



The skeleton-fibre was doubtless porous, but in all the specimens examined 

 the intimate structure of the fibre has been so obscured by secondary ci'ystal- 

 lisation that this point cannot be definitely ascertained. 



Tangential sections (Plate XXVI, figs. 5 and 6) show the cut ends of the 

 radial pillars united into a reticulation, which, though imperfect, is more complete 

 than is usual in the genus Stromatoporella. Where such sections traverse an 

 astrorhizal cylinder (as in Plate XXVI, fig. 5), then, of course, the lamina? are 

 seen as cut vertically or obliquely. Tangential sections do not exhibit the 

 incomplete or complete rings so characteristic of corresponding sections of 

 Stromatoporella granulata or S. Selwynii, and we may therefore conclude that the 

 surface did not possess the perforated tubercles of the species just mentioned. 



Vertical sections (Plate XXVI, fig. 7) show well-defined concentric lamina? 

 and short radial pillars, the latter confined to their respective interlaminar spaces, 

 or not even extending completely across these. Definite zooidal tubes cannot be 

 detected. Nine or ten lamina? occupy the space of 2 mm. measured vertically. 



Obs. — This is by far the commonest species of Stromatoporella in the Devonian 

 rocks of Britain ; and its microscopic characters enable us to separate it definitely 

 from the other species of the genus. From S. granulata, Nich., it is distinguished 



