126 PLATK XUX. 



Fig. 11. A tension spicukmi, from the interstitial 

 membranes. X 250 linear. 



ISODIOTYA EOSEA, Sowerbank. 



Vol. ii, p. 282, ' Mon. Brit. Spongiadse.' 



Fig. 12. Represents a characteristic specimen of 

 the species based on a fragment of the Rock from one 

 of the small caves of St. Catherine's Rock, Tenby. 

 Natural size. The mass of sponge occupies nearly the 

 middle of the fragment of stone. 



Fig. 13. A skeleton spiculum. X 250 linear. 



Fig. 14. One of the tension spicula, from the in- 

 terstitial membranes. X 250 linear. 



ISODICTYA INDEFINITA, BowerbanJc. 



Vol. ii, p. 286, ' Mon. Brit. Spongiadse.' 



Fig. 15. Represents the type- specimen sent to me 

 by Mrs. Griffiths. Natural size. 



Fig. 16.- One of the spicula of the skeleton. 

 X 250 linear. 



Fig. 17. A tension spiculum, from the interstitial 

 membranes. X 250 linear. 



