SPONGES. 251 



centre of the expansion in a gently curved direction to each 

 .surface. In sections the spicular mesh is somewhat irregular, 

 but the true Anthaspidellid type is often observable. (PI. VII, 

 fig. 4b.) The spicules in the spaces between the vertical canals 

 an- smaller and much more irregular, than those in the radiat- 

 inir ridges. 



The specific name is given in honor of our distinguished chief, 

 Prof. A. H. Worthen, who collected the unique example figured. 



Position find locality: In shales of the Hamilton group, asso- 

 ciated with numerous corals and bryozoa, at Thunder Bay 

 Island, Michigan. 



