﻿STROMATOPORELLA SELWYNII. 



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2. Stkomatoporella Selwynii, n. sp. PI. I, fig. 14, and PI. XXVI, figs. 2 — 4. 



The coenosteum in this species is massive or laminar, and apparently attains a 

 considerable size. The mode of attachment, in the only case observed, is by the 

 greater portion of the under surface. The laminae are gently undulated, but 

 there are no distinct astrorhizal eminences or " mamelons," nor are " astrorhizal 

 cylinders " developed. The surface is studded with numerous tubercles, of 

 different sizes, the smaller ones being imperforate, while the larger ones are blunt, 

 and have their apices pierced by round apertures (Plate XXVI, fig. 2). 

 Astrorhizae are apparently wanting, or may be incompletely developed ; but they 

 do not constitute a marked feature in the specimens examined. 



As regards microscopic structure the skeleton-fibre is thick, and is seen in 

 sections to be minutely porous. Tangential sections (Plate XXVI, fig. 3) show 

 the cut ends of the radial pillars, together with a larger or smaller number of 

 complete or incomplete rings, the latter representing sections of the hollow 

 tubercles which are developed on each successive lamiua. Vertical sections 

 (Plate XXVI, fig. 4) show very well-defined concentric laminae, of which about 

 six occupy the space of 2 mm. measured vertically. The radial pillars are well 

 developed, but are, as a rule, confined each to its own interlaminar space. 

 Imperfect zooidal tubes are occasionally recognisable, but are never conspicuous. 



Obs. — This form, as shown by the characters of the skeleton, is closely related 

 to S. granulata, Nich., and I had previously regarded it as merely a variety of the 

 latter. I am, however, now satisfied that it may be fairly considered as a good 

 species, and I have much pleasure in naming it after the distinguished Director of 

 the Geological Survey of Canada. 



Stroma toporella Selwynii is separated from S. granulata by the fact that the 

 laminae of the coenosteum are simply undulated, and the astrorhiza? are imperfectly 

 developed, the surface therefore never exhibiting the characteristic rounded or 

 conical " mamelons " of the latter species. As regards internal characters, 

 Si Selwynii is further separated from S. granulata by its markedly coarser 

 structure, as will be at once seen from a comparison of corresponding sections of 

 the two forms in question drawn to the same scale (compare figs. 1 a and 1 b of 

 Plate XXVI with figs. 3 and 4 of the same plate). From other related species of 

 the genus Stromatoporella, S. Selwynii is separated by characters essentially the 

 same as those distinctive of S. granulata, as pointed out in the observations made 

 with regard to the latter form. 



Distribution. — Not uncommon in the Corniferous Limestone of Port Colborne, 

 Ontario. S. Selwynii has not yet been certainly recognised in Britain, though 



