188 NEW YORK STATE MUSEUM 



pendent of all its neighbors in the skeletal complex, each leads an 

 individual existence. In the suborder Dictyonina, however, 

 the skeleton becomes continuous and, indeed, complicated by the 

 fusion of the spicules. The arms or rays of one unite with the 

 corresponding parts of those adjoining, and instead of having to 

 deal with a structure whose elements retain the typical hexac- 

 tine form, we find a skeleton divided into series of cubical meshes. 

 While there is generally a close adherence to this type form, yet 

 by the modification of the spicular elements there often results 

 an irregularly meshed skeleton whose derivation from the 

 hexactin is not always clear. 



The silicious sponges of the Chemung fauna have in all cases 

 yet brought under observation had their original silica replaced, 

 first by iron pyrites, which in the porous, sandy matrix has 

 changed to the peroxid of iron, and this salt for the most part 

 deoxidized and thus removed by solution or carried away in the 

 insoluble slate in suspension. There is not, thus, any way of 

 eliciting the complete spicular structure of such bodies. We 

 find their reticulate structure well exhibited on casts of exterior 

 and interior in cases where the network was strong and the 

 bundles of rod-like spicules well defined. In other cases we may 

 observe rusty traces of the original network, which manifest them- 

 selves most clearly when the specimen is moistened. At the 

 present most of the large mass of material representing these 

 fossils, which has come under observation, has been obtained 

 from surface exposures and loose blocks. Possibly fresh rock 

 from a sufficient depth may eventually afford sponges from this 

 fauna in which the pyrite of the skeleton will not have been de- 

 composed. For our present interpretation of many details of 

 structure observable in these fossils from the sandstone, we are 

 largely dependent on correlations with the pyritized skeletons of 

 dictyosponges found in the calcareous shales of the Keokuk 

 beds, at Crawfordsville Ind. • 



The specimens which we here bring forward as representatives 

 of ancient dictyonine sponges of Chemung age, present evidence 

 of a skeleton whose meshes are small and irregularly polygonal. 



