PORIFERA. 15 



Prism faces sometimes very obscurely developed toward the sum- 

 mit. Occurs as internal molds. 



Characteristic of the Chemung and occurs also in the upper 

 Portage and Keokuk. 



4. D. sceptrum Hall. (Fig. 23.) Upper Devonic. 



Elongate, usually abnormally compressed. Surface covered 



with coarse, transverse spicular bands from 10 mm. to 15 mm. 



Fig. 23. Dictyospongia sceptrum X X (Hall & Clarke, N. Y. State Mus.). 



apart and crossed by less conspicuous vertical bands about 5 mm. 

 apart. 



In the shaly sandstones of the upper part of the Chemung 

 group in New York. 



IV. Prismodictya Hall & Clarke. 

 Elongate, usually slender, gradually expanding from the acute 

 base. Surface sharply prismatic, with eight faces reticulated by 



