274 PLATE LXXXIII. 



Fig. 13. One of the small subfusiformi-acuate 

 skeleton spicula. X 320 linear. These spicula vary 

 to a considerable extent in their size. The same 

 figure also represents the tension spicula of the dermal 

 membrane. 



Fig. 14. One of the acerate spicula that are occa- 

 sionally found amongst the others. X 320 linear. 



Fig. 15 One of the large acuate skeleton spicula of 

 comparatively rare occurrence. X 320 linear. 



Fig. 16. Represents a small piece of the skeleton 

 fibre, exhibiting the numerous spicula in sitit X 150 

 linear. 



TETHEA SPINOSA, Bowerdank. 



Fig. 17. Represents the two fragments of the type- 

 specimen of the species from Fowey Harbour. Natural 

 size. 



Fig. 18. A skeleton spiculum from the radial fasci- 

 culi of the sponge. X 80 linear. 



Fig. 19. One of the tension spicula from the dermal 

 membrane. X 80 linear. These spicula vary to a 

 considerable extent in length, frequently equalling 

 those of the skeleton fasciculi. 



Figs. 20, 21, and 22. Three of the external defen- 

 sive and retentive spicula. X 530 linear. No two of 

 these spicula have the same form or mode of disposi- 

 tion of the spines. 



DESMACIDON JIGAGEOPILA, Boiverbank. 



Vol. ii, p. 352, 'Mon. Brit. Spongiadae;' iii, pi. Ixiii, figs. 814. 



MICEOCIONA JECUSCULUM, Bowerbank. 

 Plate LXXXIII. 



Hymeniacidon jecusculum, Bowerbank. Vol. ii, p. 198, ' Mon. 



Brit. Spongiadse.' 



A re-examination of the type-specimens of this sponge 



