286 PLATE LXXXV. 



HYMENIACIDON MEDIUS, Bowerbank. 



Fig. 11. Represents the type-specimen based on a 

 rolled pebble. Natural size. 



Fig. 12. An average-sized acuate skeleton spicu- 

 lum. X 250 linear. 



Fig. 13. One of the tension spicula of the dermal 

 membrane. X 250 linear. 



DESMACIDON TNCOGNITUS, Bowerbank. 



Fig. 14. Represents the type-specimen. Natural 

 size. 



Fig. 15. An average-sized, acuate, skeleton spicu- 

 lum. X 250 linear. 



Fig. 16. One of the tension spicula of the dermal 

 membrane. X 250 linear. 



ISODICTYA FILAMENTA, 



Plate LXXXV. 



Sponge. Branching, ascending from a slightly ex- 

 panded base. Surface smooth. Oscula and pores 

 inconspicuous. Dermal membrane spiculous ; spicula 

 acerate, rather slender, very numerous, dispersed or 

 subfasciculated. Skeleton, Primary lines radiating 

 from the base of the sponge upwards; bi- or tri- 

 spiculous ; secondary lines uni-spiculous ; rete rarely 

 more than one spiculum wide. Sarcode abundant. 



Colour. In the dried state, dark green. 



Habitat, Shetland ; Mr. C. W. Peach. 



Examined. In the dried state. 



This interesting little species was dredged at Shet- 

 land in 1866 by Mr. Peach. It had grown on a frag- 

 ment of a dead shell 9 lines in length by 4 lines in 

 width. The sponge is 5 lines in height, and does not 

 exceed an ordinary sewing thread in thickness, and it 



