INTRODUCTORY. 



Preliminary Memarhx. Tlie purpose of this Avork is to present an 

 account of some palaeozoic forms of an extinct group of organisms, repre- 

 senting the ''glass-sponges" of existing seas. Certain simple structures 

 known as Protospongia which occur in the Cambrian and early Silurian 

 faunas, have for many years been looked upon as examples of such siliceous 

 sponges, notwithstanding the fact that their skeletons have been wholly 

 replaced by other substances, but until a comparatively recent period the 

 interesting division of these fossils here designated as a distinct family, was 

 unknoAvn or unrecognized as sponges in palaeozoic faunas. The earliest form 

 recorded was looked ujjon by its discoverer, Mr. T. A. Conrad, as a cephalopod 

 shell, and ^vas so described in 1842, under the name Hydnoceras tuherosuni. 

 This sj)ecimen was from the Chemung rocks of Steuben county, N. Y. At 

 the same date, a wholly distinct form from the same geologic fomiation was 

 described by Mr. Laudneu Vanuxeh as Upliantceaia Chemungensis and was 

 regarded by him as a marine plant. This interpretation of the nature of such 

 bodies became current for the time, and was expressed in the term Diciyo 

 pJiyton, which was subsequently applied to several species from the upper 

 Devonian and Waverly horizons. Although the species which had been 

 described up to the year 1880, manifested considerable diversity of form, their 

 condition of preservation did not readily suggest their real nature. In all 

 instances the delicate skeleton of the sponge had been dissolved and had 

 disappeared, leaving only internal and external casts of the bodies 

 with more or less distinct impressions of the spicular network. Such 

 markings were believed to be comparable to those occurring in some of the 

 living marine algae and this similarity, in the absence of any recognized agree- 

 ment with other known organisms, was the basis of the interpretation of their 

 nature as then made. The discovery of bodies of a similar character in the 

 calcareous shales of lower Carboniferous age at Crawfordsville, Indiana, 

 revealed a spicular skeleton, all the parts of which had been changed to iron 

 pyrites, but -were not otherwise materially modilied. The study of this 

 material elicited the first definite evidence of relationship of these bodies to 



