24 PLATE X. 



the transverse interlacing secondary parts of the 

 skeleton, in the intervals between which are seen the 

 pores in an open state, congregated in the porous areas 

 of the dermal membrane. X 150 linear. 



This specimen, in conjunction with that from the 

 distal end of the cloaca of P. ornata, Plate IX, fig. IG, 

 exhibiting the nature and structure of the excurrent 

 organs, afford us a most satisfactory view of the mode 

 of the general structure of the sponges of this interest- 

 ing genus. 



Fig. 7. — One of the large superfusiformi-acuate, 

 skeleton spicula. X 80 linear. 



Fig. 8. — One of the spinulate, external, defensive 

 spicula. X loO linear. 



The porous areas of P. bidhoxa are somewhat different 

 from those of P. robusta. The dermal membrane is 

 much more delicate in its structure, and the number of 

 pores in each are less. Those represented by fig. 2 are 

 from the bulbous portion of the sponge. 



