14 BRITISH STROMATOPOROIDS. 



In 1873, Mr. Salter expressed the opinion that Stromatopora is " a very solid 

 calcareous Sponge" (' Cat. Sil. Foss.,' p. 99). 



In the same year, the present writer described (' Ann. and Mag. Nat. Hist.,' 

 ser. 4, vol. xii) several Stromatoporoids from the Silurian and Devonian Rocks of 

 Canada. In one of these, viz. Clathrodictyon (Stromatopora) ostiolatum, Nich., the 

 presence of regularly-disposed round apertures of large size was pointed out, and 

 it was suggested that these corresponded with the " oscula " of Sponges. 



In 1874, the present writer further discussed (' Ann. and Mag. Nat. Hist.,' 

 ser. 4, vol. xiii) the affinities of the Stromatoporoids, referring them to the Galci- 

 spongiai, and indicating the presence in various species of large openings, which 

 might be regarded as of an "oscular" nature. The skeleton was regarded as 

 " composed of an amalgamated system of horizontal spicules, separated by inter- 

 spaces, and kept apart by a vertical system of delicate calcareous rods, giving rise 

 to a system of more or less quadrangular tubes." In the ' Report on the Palaeon- 

 tology of the Province of Ontario ' (1874) the same opinion is repeated. In the 

 ' Palaeontology of the State of Ohio ' (vol. ii, 1875) the writer described 

 several species of Stromatoporoids from the Devonian Rocks of Ohio, and proposed 

 two new genera under the names Sijringostroma and Dictyostroma. The type of 

 Syrmgostroma is the singular S. densum, which possesses the reticulated skeleton 

 characteristic of Stromatopora, Goldf ., but which has certain peculiarities of its own. 

 I shall later on discuss the value of these peculiarities. Besides S. densum, Nich., 

 another remarkable form was placed under Sijringostroma, under the name of 

 S. columnare, Nich. This latter, however, is really quite distinct in its structure, 

 and forms the type of the genus Stylodictyon, Nich. and Mur. The genus Dictyo- 

 stroma was proposed for a remarkable Stromatoporoid from the Silurian Rocks of 

 Kentucky ; but as the minute structure of the skeleton is still unknown, it is 

 doubtful whether this genus can be retained. 



In the 'Dawn of Life' (1875), Principal Dawson incidentally gives the result 

 of his observations on the structure of Stromatopora and its allies, regarding them 

 as connected on the one hand with the Forcminifera and on the other hand with 

 the Sponges. He compares the astrorhizal tubes of certain Stromatoporoids with 

 the " canal-system " of Eozoon. 



In a memoir upon the genus Stauronema, Prof. Sollas (' Ann. and Mag. Nat. Hist.,' 

 ser. 4, vol. xix, 1877) places Stromatopora among the Vitreo-hexactinellid Sponges. 

 In a subsequent paper (' Quart. Journ. Geol. Soc.,' 1877), the same author 

 expresses the opinion that under the head of Stromatopora are included organisms 

 of very different affinities, some being Siliceous Sponges, some related to Mille- 

 pora and Hydractinia, and some with relationships as yet undetermined. 



In 1877, Mr. Carter expressed the opinion (' Ann. and Mag. Nat. Hist.,' ser. 

 4, vol. xix) that the Stromatoporoids are closely related to the living Hydractinia, 



