PLATE LVI. 143 



on which it is parasitical. Most frequently the sponge 

 is very nearly concealed amidst the numerous branches 

 of the plant. 



ISODICTYA ALDERI, Bowerbank. 



Vol. ii, p. 323, ' Mon. Brit. Spongiadce.' 



Fig. 20. Represents the largest of three specimens 

 of this sponge found at Salcombe Bay, and sent to me 

 by Mr. Alder. Natural size. 



Figs. 21 and 22. Represent two specimens which 

 I found at Mill Bay, near the Landsend, Cornwall, in 

 May, 1859. A third specimen, which I obtained at the 

 same locality, very closely resembles the one repre- 

 sented by figure 20. Natural size. 



Fig. 23. One of the skeleton spicula. X 250 

 linear. 



Fig. 24. A slender, acuate, tension spiculum, from 

 the interstitial membranes. X 250 linear. 



Figs. 25 and 26. Two of the dentato-palmate, 

 equi-anchorate, retentive spicula, from the dermal 

 membrane. 



