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. — Eepresents a small piece of the skeleton 

 fibre, exhibiting the numerous sjoicula in situ. X 160 

 linear. 



Tethea spinosa, Boinerljcmh. 



Fig. 17. — Eepresents the two fragments of the tyjDe- 

 spccimen 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 iEGACiROPiLA, Bowcrhanli. 



Vol. ii, p. 352, ' Mon. Brit. Spongiadaj;' iii, pi. Ixiii, figs. 8—14. 



MiCEOCiONA JECUSOULUM, Bowevbank. 

 Plate LXXXIII. 



Rijmcmacidon jecuscvhm, Bowcrbank. Vol. ii, p. 19S, ' Mou. 

 Brit, Spougiada:.' 



A ro-oxamination of the type-specimens of this sponge 



