66 



each other, so that some spicules appear to have seven arms 

 radiating from the central node instead of the normal number. 

 The sponges of this genus are cup shaped with a thin sur- 

 face membrane which is provided with regularly disposed 

 canal openings. Fragments of the skeleton are not uncom- 

 mon and are readily distinguished from all the other hexac- 

 tinellid remains in this flint by the large size of the mesh as 

 well as by its irregular arrangement. 



Leptophragma sp. 



(Plate V, fig. 1 8). 



Mesh work of the skeleton arranged so as to form triangu- 

 lar and quadrangular interspaces. The central knot of the 

 spicule solid and expanded to about twice the thickness of 

 the arms. Average diameter of the mesh 1,09 mm.; thick- 

 ness of the arms of spicule 0,04 mm. ; of the central node, 

 0,09 mm. 



The much smaller size of the mesh work and the infla- 

 tion of the central node of the spicule distinguish these frag- 

 ments of sponge from the preceding form. 



Craticularia sp. 



(Plate V, fig. 19). 



Mesh skeleton very regular and disposed so as to form 

 quadrangular interspaces. The central nodes are solid, and but 

 slightly larger than the spicular arms. Thickness of the arms 

 0,033 mm.; diameter of the squares or distance between the 

 nodes 0,2 mm. Rare. 



In the regularity and form of the interspaces of the mesh 

 and the character of the nodes, this sponge bears a great re- 

 semblance to specimens of Craticularia from Streitberg which 

 are in the Museum at Munich. Prof. Sollas has also descri- 



