234 Dr. H. A. Nicholson on some neiv or 



are incompletely developed and are rather of the nature of a 

 loose reticulation. 



Ohs. I sliall describe this species more fully hereafter. It 

 is distinguished from most of the members of the genus by 

 the delicacy of the skeletal tissue, the radial pillars being 

 exceedingly delicate, and also by the loosely reticulate character 

 of the concentric laminae (PL VII. fig. 4). It is also charac- 

 terized by the general regularity of the hexactinellid raeshvvork 

 displayed in tangential sections (PI. VII. fig. 3). A. inter- 

 textum is undoubtedly closely allied to A. Schmidtii, Rosen ; 

 but, for the reasons previously stated, I think it must in the 

 meanwhile be regarded as a distinct species. 



The above brief diagnosis of the species is founded upon 

 British specimens. I have, however, collected examples from 

 the Silurian deposits of Esthonia, which seem to be only a 

 variety of this species, and I have figured tangential and 

 vertical sections of one of these (PI. VII. figs. 5 & 6). The 

 tangential sections of the Russian examples differ from cor- 

 responding sections of British specimens in the much less 

 complete character of the " hexactinellid " mesh work, which 

 is sometimes hardly recognizable at all, only the cut ends of 

 the pillars being visible. This incomplete character, or appa- 

 rent absence, of the horizontal " arms " can, however, hardly 

 be due to anything save imperfect preservation. Vertical 

 sections (PI. VII. fig. 6) show the same general structure as 

 corresponding sections of British specimens ; but the radial 

 pillars are decidedly more closely set and the concentric 

 laminge are more completely developed than in the latter. 

 If it should appear to be desirable to indicate these apparently 

 constant differences by a special name, the Russian examples 

 may be called A. intertextum, var. suevicum. 



Formation and Locality. Not very uncommon in the Wen- 

 lock Limestone of England (Ironbridge, Much Wenlock, 

 Dudley). The Russian examples are from the Silurian 

 Limestones (zone of Pentamerus esthonus) of Kattentack, 

 Esthonia. 



StromatoporeUa'* laminata, Barg., sp. 

 (PI. VII. figs. 9 and 10.) 



Diapora laminata, Bargatzkv, Die Stromatoporen des rheinisclien 

 Devons, p. 60 (1881). 



The coenosteum forms a laminar expansion, often of con- 

 siderable size, wliich is usually attached by a single point, 



* The genus StromafojioreUa, Nicb. (Mon. Brit. Strom, p. 92) includes 

 Stromatoporoids which resemble the species of Strotnatopora, Goldf. 

 (properly so called), in having a porous or tubulated skeleton-fibre, but in 



