STROMATOPORA TYPICA. 173 



1873) as Coenostroma incrustans (Plate III, fig. 6) ; but it is by no means probable 

 that these species are identical. The other point which seems to distinguish 

 8. Hudsonica from 8. typica is that the zooidal tubes of the former seem to be 

 provided with very few tabulas ; but much stress cannot be laid upon this, as my 

 specimens are in a state of poor preservation. Upon the whole, it may at present 

 be concluded that 8. Hudsonica, Dawson sp., is specifically distinct from S. typica, 

 Rosen, though certainly nearly related to it. 



Mr. Whiteaves has also supplied me with a fragment of the original specimen 

 described from the Guelph Limestoues (Niagara Group) of Canada by Sir J. W. 

 Dawson under the name of Coenostroma galteuse (' Life's Dawn on Earth,' p. 160, 

 1875, and ' Quart. Journ. Geol. Soc.,' vol. xxxv, p. 52, 1879). The minute 

 structure of this specimen is practically destroyed by dolomitisation, but all its 

 general characters would lead to the belief that it is very closely related to 8. typica, 

 Rosen, and is probably absolutely identical with it. 



Prof. J. W. Spencer has kindly supplied me with a fragment of the species 

 which he described from the Niagara Limestone of North America under the name 

 of Coenostroma constellatum ('Niagara Fossils,' p. 48, pi. vi, fig. 11, 1884). 

 The minute structure of this is also almost wholly destroyed by dolomitisation ; 

 but it does not appear to be in any way distinguishable as regards its general 

 characters from Gceaostroma galtense, Dawson, and I am strongly disposed to think 

 that it is really identical with 8. typica, Rosen. 



If the above view should prove to be correct, then Coenostroma galtense, Dawson, 

 and C. constellatum, Spencer, must be considered as synonyms of 8. typica, 

 Rosen. Prof. Spencer, however, identifies his species with the previously described 

 Stromatopora constellata of Hall (' Pal. N. Y.,' vol. ii, p. 324, pi. lxxii, fig. 2 a, b, 

 1852). If the identity of this last with S. typica, Rosen, should also be proved, 

 then Hall's name should, strictly speaking, have precedence over that of Rosen. 

 The real nature of Hall's Stromatopora constellata could, however, be established 

 only by an investigation of the original specimen, if even then ; since the 

 brief description, with its accompanying figures, is not sufficient to establish 

 clearly so much as the generic position of the fossil. Under these circumstances 

 it would appear unreasonable to abandon the name of 8. typica for that of 

 8. constellata, even were the identity of the two to be ultimately proved ; since 

 Rosen based his species upon well-preserved specimens, and illustrated its 

 characters by admirable and thoroughly recognisable figures. 



Distribution. — Stromatopora typica, Rosen, appears to be wholly confined to 

 the Silurian (Upper Silurian) Rocks, of which it is by far the commonest and most 

 characteristic Stromatoporoid. No Ordovician or Devonian examples of the 

 species are known. The species is, in fact, an essentially Wenlock type, and has 

 an extremely wide distribution iu space. In the Wenlock Limestone of Britain 



