STROMATOPORELLA GRANULATA. 203 



vermiculate ridges. Parts of the surface may be covered by a thin calcareous 

 membrane, which is perforated by scattered circular apertures (Plate IV, fig. 6). 



As regards its internal structure, the skeleton-fibre is minutely porous, or is 

 penetrated by delicate canaliculi (Plate I, figs. 4 and 5) ; while the general 

 ccenosteal tissue is of the incompletely reticulated type. Vertical sections 

 (Plate I, fig. 5, and Plate VII, fig. 6) show well-developed " concentric lamina?," 

 each of which commonly exhibits a median clear line. The apparent "lamina " 

 of vertical sections (Plate XXVI, fig. 1 b) represent the regularly developed 

 connecting processes of the radial pillars ; the latter structures being short and 

 usually discontinuous, being commonly confined to the interlaminar space in 

 which they originate. From eight to ten concentric lamina? occupy the space of 

 2 mm. measured vertically. Imperfect zooidal tubes, with remote tabula?, are 

 sometimes recognisable, but, in general, vertical sections do not clearly exhibit 

 the presence of such structures in a definite form. In tangential sections (Plate I, 

 fig. 15; Plate XXVI, fig. 1 a) the perforated tubercles of the successive lamina? 

 are abundantly seen, each in the form of a more or less complete ring, enclosing a 

 central space. Occasionally the intervals between the cut ends of the radial 

 pillars are crossed by delicate partitions, indicating the presence of astrorhizal 

 tabula? or " interlaminar septa.'' 



Obs. — Having now fully examined my available material, I have come to the 

 conclusion that the Devonian rocks of North America contain two allied but 

 nevertheless really distinct species of Stromatoporella, which up till now I have 

 included under the single name of 8. granulata. One of these — the true 

 8. granulata — occurs in the Hamilton formation, and I have supplemented the 

 figures of its microscopic structure with a drawing of an actual specimen (Plate 

 XXVI, fig. 1). The other form in question occurs in the Corniferous Limestone 

 of Canada ; and I shall briefly describe it under the name of 8. Selwynii, Nich. 

 Neither of these forms can be positively asserted to occur in the Devonian rocks 

 of either Britain or Germany, though from both of these regions I have examples 

 of closely related if not identical types. 



As regards its general characters, 8. granulata, Nich., as here restricted, is 

 distinguished by its laminar ccenosteum, its non-parasitic habit, and its epithecate 

 under surface. The upper surface always exhibits well-marked astrorhizal 

 prominences or " mamelons " (Plate XXVI, fig. 1), and is always studded with 

 numerous tubercles, of which the larger have apertures at their apices. 1 



1 In the heading to this description of S. granulata, fig. 14 of Plate I is inadvertently quoted as 

 illustrating the surface-characters of the species. In the explanation to Plate I this same illustration 

 is likewise ascribed to S. granulata. This figure, however, really belongs to the form which I now 

 name 8. Selwynii, which in surface-characters closely resembles 8. granulata. Fig. 6 of Plate IV is 

 illustrative of the surface of the true S. granulata. 



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