Explanations of Platks. 201 



Figure 15. One of the two largest of the specimens in this gioup, enlarged; 

 showing the ])eripheral spicules, and the cruciform spicules over a 

 part of the wall. The surface is a continuous pyrite film with an 

 in-egular bi-eak near the centei", due to the adhesion of a part of 

 the film to the opposite side of the matrix. Tlie specimen from 

 which these two drawings have been mad(^ was loaned for the 

 purpose by the U. S. National Museum and is one of the speci- 

 mens upon which Rauff based his conception of the genus 

 Teganium. X 3. 



Figure 10. Another group of young examples. 



Figure 17. One of these enlarged, showing long peripheral spicules and a 

 continuous surface film, x 3. 



Figure 18. A normal mature specimen, natural size. This specimen is in 

 the condition of ] )reservation usual for this species, the sponge 

 having separated in such a manner as to expose the inner poriferous 

 wall of the reticulum, and the outer wall in peripheral section. 

 The rest of the latter adheres to the separated portion of the 

 matrix. 



Figure 19. An enlargement of a portion of the inner wall, showing the 

 areoles enclosed by a net-work of irregularly arranged cruciform 

 spicules. X 3. 



Figure 20. A portion of the outer wall of the sponge, showing a regular 

 reticulation, the matrix beneath bearing obscure traces of the areoles 

 of the inner layer, x 3. 



Figure 21. An enlargement of a portion of the surface similar to that 

 shown in figure 19. x 3. 



Figure 22. Part of a segment of one of these spheres, showing a portion of 

 the inner wall, and the section of the outer wall, x 3. 

 All the specimens here figured are from the Utica slate at 

 Holland Patent, New York. 



