imperfectly -known Species of Stromatoporoids. 313 



rous minute pointed " mamelons," each of which is 

 perforated at its summit by the aperture of the axial 

 canal of one of the astrorhizal systems. 



c The centres of the astrorhizaa are considerably closer 

 together than in 8. typica, in which species they are 

 usually from 5-6 millim. apart. 



d. The zooidal tubes are furnished with fewer tabula? 

 than those of S. typica, and also communicate more 

 freely, giving to vertical sections a more lax and open 

 aspect. The apparent scanty development of tabulae 

 may, however, be the result of poor preservation. 



e. The skeleton-fibre is a little coarser and the skeletal 

 network is not quite so fine as in 8. typica. 



Upon the whole therefore, and in view of the above-men- 

 tioned distinctions, I am disposed to regard 8. hudsonica as 

 a good species. It is, however, obviously closely related to 

 S. typica, Rosen, and may be considered as representing this 

 common European species in the Silurian rocks of the New 

 World. 



Formation and Locality. Silurian formation, Albany River, 

 Hudson's Bay, and Cape Churchill. The fragments upon 

 which the above description has been drawn up were fur- 

 nished to me by Mr. Whiteaves, and the specimens from 

 which they were taken were collected in 1878 by Prof. R. 

 Bell. The specimen from Albany River is the one upon 

 which Sir W. Dawson originally founded his Caunopora 

 hudsonica ; but its preservation is not so good as that of the 

 example from Cape Churchill. 



Stromatopora, sp. 

 (Cf. S. biicheliensis, Bargatzky, sp.) 



Two specimens in the collection of the Geological Survey 

 of Canada, from the Devonian rocks of Lake Winnipegosis, 

 have the general aspect of Stromatopora biicheliensis, Barg., 

 sp., and are probably referable to this species. Unfortunately 

 the specimens in question are dolomitized, and their internal 

 structure is so far altered that this reference cannot be regarded 

 as free from doubt. 



8. biicheliensis is distinguished from 8. Hiipschii, Barg., 

 sp., its nearest ally, by its comparatively fine skeleton-fibre 

 and correspondingly close texture, and by the smaller size and 

 greater remoteness of the astrorhizae. I have elsewhere fully 



