76 



EXPLANATION OF PLATE VI. 



Fig. 1 . Pachymatisina Johnstonia. 



Fig. 2. Stellate spicula, occurring in the fleshy substance of Pachymatistna Johnstonia. 



Figs. 3 & 4. Two varieties of spicula of Pachymatistna Johnstonia. 



Fig. 5. Tri-radiate spiculum of Pachymatistna Johnstonia. 



a. Bifurcation of one of the radii. 

 Fig. 6. A portion of a large cylindrical spiculum of Pachymatisma Johnstonia. 



a. Hemispherical termination. 

 Fig. 7. Minute tuberculated spicula attached to a fragment of a large cylindrical 



spiculum. 

 Fig. 8. Central canal of the spiculum. 

 Fig. 9. Duseideia KirkiL 

 Fig. 10. Portion of a fibre of Duseideia Kirkii, exhibiting grains of sand imbedded 



in its substance. 

 Fig 1 1 . Duseideia fragilis, (Johnston). 

 Fig. 12. Fibre of Duseideia fragilis, rendered opaque by the number of grains of 



sand imbedded in its substance. 

 Fig. 13. A smaller fibre of the same species of sponge, showing tlie grains of sand 



to be fewer in number, and disposed nearly in the centre of the fibre. 



EXPLANATION OF PART OF PLATE VII. 



Fig. 1. Commonest form of spiculum of Duseideia Kirkii. 

 Fig. 2. Spiculum of Duseideia Kirkii, with oval base. 

 Fig. 3. Spiculum of Duseideia Kirkii, with globular base. 

 Fig. 4. Tuberculated spiculum of Duseideia Kirkii. 

 Fig. 5. Large multi-radiate spiculum of Duseideia Kirkii. 

 Fig. 6. Curved spicula of Duseideia Kirkii. 



