ON FOSSIL SPONGES PEOM METIS. 47 



ture of the spougc-wall in the fossil aud iu the original specimeus described by Schulze, 

 now in the British Museum of Natural History. 



The whole of the spicules, in the Utica as in the Quebec group specimens, are com- 

 pletely pyritised, and appear iiuder the microscope to be made up of rows of cubical 

 crystals of pyrites. They were probably originally siliceous, but this need not excite 

 surprise, as the silica of such spicules is in a condition which facilitates solution, and in 

 some modern sponges the spicules are not purely siliceous, but contain some animal matter. 

 I hare also noticed other cases in which siliceous Palseozoic sponges have experienced this 

 change, while in many specimens the spicules have entirely disappeared. 



This is the case with the Erian or Devonian sponges of the genus Didyophyton and 

 allied genera, which, owing to their apparently membranous character, I at one time 

 believed to be fucoids, but abandoned this idea on seeing the specimen of Uphantœnia 

 (Physospongia, Hall), which Prof. Whitfield was kind enough to show me in the New 

 York Museum iu July, 1881. In a note communicated to Prof Whitfield iu August, 

 1881, I have made the following remarks on the pyritisation of sponges : — 



" The most puzzling fact in connection with the original siliceous character of these 

 sponges is their mineral condition, as being now wholly replaced by pyrite. Carbonaceous 

 structures are often replaced in this way, and so are also calcareous shells, especially 

 when they contain much corneous matter, but such changes are not usual with siliceous 

 organisms. If the spicules were originally siliceous, either they must have had large 

 internal cavities which have been filled with pyrite, or the original material must have 

 been wholly dissolved out and its place occupied with pyrite. It is to be observed, how- 

 ever, that in fossil sponges the siliceous matter has not infrequently been dissolved out, 

 and its space left vacant or filled, with other matters. I have specimens of Astylospongia 

 from the Niagara formation which have thus been replaced by matter of a ferruginous 

 color ; and in a bundle of fibres, probably of a sponge allied to Hyalomena from the Upper 

 Llaudeilo of Scotland (since named Hyalostelia by Hinde'), I find the substance of the 

 spicules entirely gone and the spaces formerly occupied by them empty. It should be 

 added that joints of Crinoid stems and fronds of Fenestella occurring in the same specimen 

 with the Uphantsenia are apparently in their natural calcareous state." 



The type of structure of Cyathophycus is essentially that of the Hexactinellid sponges 

 of the suborder Dictyonina of Zittel, and under this, as has already been suggested by 

 Barrois, it belongs to the family of Dictyospoiigidœ, established by Hall for Dictyophyton 

 and the allied sponges of the Erian rocks. This type, already known as far back as the 

 Utica shale, is now carried a stage farther by our discoveries at Metis. 



The sponges of the genus Cyathophycus are not abundant in the beds explored at 

 Metis and most of them have been much broken up. Only one specimen was obtained 

 as a tolerable state of completeness. 



Genus ACANTHODICTTA, Hinde. 



Sponges approximately subcyliudrical in form, consisting of a skeletal mesh-work 

 of longitudinal and transverse spicular strands or fibres. The longitudinal strands are 



' I have similarly explained Pi/rilonema of McCoy and Eophylon explanalum of Hicks, as has Hinde also, in 

 Geol. Mag., 1886. 



