Neto Species of Sponges. 



51 



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oblique and rhombi '.dal in the snecimons, but this is pro- 

 bably due to pressui'e. The hori-jo tal spicules seem to be 

 triacerate in form, and much shorter than those of the ver- 

 tical system, though of very different lengths. They are 

 sometimes in bundles and sometimes solitary. 



In parts of the substance, apparently within the reticulate 

 wall, may be seen a few cruciform spicules, and floccu- 

 lent patches apparently of very email spicules, which seem 

 to have been mostly internal and most abundant toward the 

 base, but cannot be distinctly made out. ' 



The whole of the spicules are completely pyritized, and 

 appear under the microscopo to be made up of rows o^ 

 cubical crystals of pyrites. They were probably originally 

 siliceous, but this need not excite sui-prise, as the silica of 

 such spicules is in a condition which facilitates solution, 

 and in some modern sponges the spicules are not purely 

 silicious, but contain some animal matter. I have also 

 noticed other cases in which silicious palaeozoic 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 Dictyophpton and allied genera, which, owing to 

 their apparently membranous character, I at one time be- 

 lieved to be fucoids. but abandoned this idea on seeing the 

 specimen of Uphantenia (Physospongia, Hall) which Prof. 

 Whitfield was kind enough to show me in the New York 

 Museum in July, 1881. In a note communicated to Prof. 

 Whitfield in August, 1881, I have made the following 

 remarks on the pyritization of sponges : — 



" The most puzzling fact in connection with the original 

 silicious character of these sponges is their mineral condi- 

 tion, as being now wholly replaced by pyrite. Carbonaceous 

 structures are often I'eplacod in this way, and so arc also 

 calcareous shells, especially when they contain much cor- 

 neous matter, but such changes are not usual with silicious 

 organisms. If the spicules were originally silicious, either 

 they must have had large internal cavities which have been 

 filled with pyrite, or the original material must have been 



