imperfectly-known Species of Stromatoporoids. 31 5 



distinct or may become laterally confluent, and thus give rise 

 to sinuous loops. 



Obs. This species was originally based upon specimens 

 from the Wenlock Limestone of Britain, and it has not 

 hitherto been certainly recognized elsewhere. The Silurian 

 rocks of Oesel yield, however, a closely allied form, which I 

 have provisionally named Stromatopora borealis, and which I 

 may figure and briefly describe here. These two forms agree 

 with one another in the main details of their minute structure, 

 but they differ, amongst other points, in their mode of growth 

 and in the relative development of the astrorhizse. In the 

 typical S. Carieri, Nich., the coenosteum is massive and 

 astrorhizse are altogether wanting or are most imperfectly 

 developed ; whereas in S. boreal is, Nich., the coenosteum is 

 laminar and astrorhizse are extensively developed. The single 

 Canadian specimen which I possess is a fragment only ; but 

 it appears to be a portion of a massive specimen, and it shows 

 no definite astrorhizse, and I therefore refer it to S. Carteri. 



Formation and Locality, The only Canadian example I 

 have seen is from a loose boulder of Silurian age, from Hayes 

 River, Hudson's Bay (coll. R. Bell, 1878). 



Stromatopora borealis, Nich. (PI. IX. figs. 7 and 8.) 



The coenosteum in this species forms flat laminar expan- 

 sions, attaining when mature a diameter of several inches, 

 with a thickness of from a centimetre or less to more than 2 

 centimetres. The under surface was covered by an epitheca, 

 and was attached by a limited point to some foreign body. 

 The skeleton-fibre is thick and coarsely porous, and the 

 skeletal tissue is of the completely reticulate type, while the 

 mode of growth is not latilaminar. 



The surface exhibits vermiculate ridges, which inosculate 

 with one another so as to form a coarse network corresponding 

 with the reticulated skeleton, the elongated or rounded meshes 

 of the network corresponding with the apertures of the more 

 or less confluent zooidal tubes. The surface also shows very 

 well developed, ramified astrorhizse, which do not open upon 

 definite " mamelons," and which have their centres from 10 

 to 12 millim. apart. 



Tangential sections (PI. IX. fig. 7) show the vermiculate 

 skeletal network, with sinuous and often elongated meshes 

 representing rows of confluent zooidal tubes. Vertical sections 

 (PI. IX. fig. 8) show stout, flexuous, radial pillars, united by 

 irregular, oblique, and equally stout connecting-processes, and 

 separated by the zooidal tubes. About six pillars with their 



