SoLLAS — HexactineUid Sponge from the GauU, 8^c, 445 



Horizon. Lower Gault. 



Locality. Cambridge. 



Remarks. Of cretaceous sponges this most nearly resembles 

 Graticularia vulgata, Pocta, and C. zitteli, Pocta, but differs partly 

 in shape, since it does not expand at the base, as both these sponges 

 do, and partly in the size of the oscules, which, judging from com- 

 parison with Pocta's illustrations, are larger than those of C. vul- 

 gata and smaller than those of C zitteli. The inner surface is, 

 however, very similar to that of C. vulgata. The skeleton, or what 

 indications remain of it, appears to have been characterized by 

 much slenderer or thinner fibres than occur in Pocta's species. The 

 sponge is mineralized with iron pyrites, in the far from common 

 form of simple octahedra, the faces, edges, and quoins of which 

 project in all directions from both surfaces. In the interior, as 

 shown by slicing, other faces as well as those of octohedra occur ; 

 they are striated in a marked manner, and may indicate the pre- 

 sence of marcasite. 



The radial canals are nearly all filled with pyrites, but some 

 for a short distance remain vacant, running straight across the 

 wall. The skeleton has disappeared ; its traces remain as hollow 

 casts, which are only visible here and there ; they may be distin- 

 guished from accidental cracks by their parallel-sidedness, rounded 

 surface, and sometimes by their regular rectangular cross- like form. 



I believe this is the first instance not only of the description of 

 a fossil sponge from the Gault, but of the observation of traces of 

 skeletal remains in a wholly pyritized specimen. 



\For Explanation of Plate, see next page.'] 



