408 REVISION OF THE NORTH AMERICAN PORIFER^. 



Explanation of Plate xiii. 



Figs. 1, 2. 7. Dendrospongia crassa. 



Fi"'. 1. Single fibre x 8 showing the interior, witli lining deposit, concentric form of this deposit, and what 

 appeared to be a particle of foreign matter imbedded in the interior.. The concentric structure of the horny 

 walls is well shown in this and in figure "2. 

 Fig. 2. Section of same fibre x 8- 



Skeletal supports of one fistular projection or projecting excurrent orifice of a solid specimen. Nat- 

 Figs. 11, 19, 20. Verongia Jistularia. 



Section of skeleton, natural size of variety ajjplicata. 



Portion of the same X 8 showing the growth of new fibres externally and the irregular character- 

 istics of the anastomosis of the fibres, also their round form by the accompanying transverse section "a". 



Fio-. 20. Reduced to two thirds natural size of specimen, combining characteristics of varieties fistularis 

 and rupicola "d" and applicata "a" and/wfoa "b, c". 



Figs. 3, 4, 5, 6. Aplysina aurea Hyatt. 



Fig. 3. The side of one of the honeycomb-shaped cells, natural size. 



Fig. 4. The same X 8 in outline merely, the internal tube is not drawn. 



Fig. 5. Transverse sections of dried fibre sjiowing variation in form. 



Fig. 6. Broken fibre exhibiting the lining very fnuch contracted, twisted and projecting beyond the end "a". 



Figs. 12, 15. Aplysina pi'cetexta Hyatt. 



Natural size of the side of one of the cells. 



A piortion x 8. 



Figs. 8, 9, 14. Aplysina gigantea Hyatt. 



Natural size of the side of one of the cells. 

 A portion of Fig 14 X 8. 

 ^ Sections of fibres showing the variation of form. 



Figs. 10, 16. Aplysina cerophoha Nardo. 



Fig. 10. Natural size. 



Fig. 16. X 8. 



Figs 13, 17, 18. Aplysina cellulosa Hyatt. 



Fig. 13. Side of one cell, natural size. 



Fig. 17. Shows thickness of some of the fibres and the comjilete filling up of some of the smaller meshes 

 on the left of the figure by the external concentric deposits of keratose"a". 



Fig. 18. Exhibits the solid filling of granular yellow matter, which is found in this and many other species 

 of the Aplysinae, projecting from a broken tube. 



