382 A MONOGRAPH OF THE 



frequently in the latter than in the former position. 

 Although tolerably abundant in the skeleton, I did not 

 succeed in finding either of these forms in the reticular 

 structure of the dermal membrane. The proportions of the 

 sub-fusiformi-acerate spicula are as follows : length 535th 

 inch, diameter ^i^rd inch. 



I have not been fortunate enough to have seen any other 

 good example of this species. On a pebble from Shetland, 

 sent to me by the late Mr. Barlee, there is a small thin 

 patch of the sponge not thicker than a sheet of paper, and 

 of about three lines in diameter. 



6. IsoDiCTYA ROSEA, Bowerbank. 



Sponge. Coating. Surface uneven, minutely hispid. Os- 

 cula dispersed, large ; simple, slightly elevated or sub- 

 fistulous. Pores inconspicuous.' Dermal membrane 

 pellucid, very thin, aspiculous. Skeleton, slender and 

 delicate ; spicula acerate, short, and rather stout. 

 Interstitial membranes. Spicula acerate, slender, not 

 very abundant. Sarcode abounding in vesicular 

 cells. 



Colour. — Alive, delicate rose-pink. 

 Locality. — St. Katherine's Rock, Tenby ; Guliot Caves, 

 Sark ; J. S. Bowerbank. 



Examined. — Alive . 



This delicate and fragile species is abundant at Tenby, 

 in the small cave, about the middle of the north side of 

 St. Katherine's Island. In the Guliot Caves at the Island 

 of Sark it is rather of rare occurrence. It rarely exceeds 

 two inches in diameter, and from a quarter to half an inch 

 in thickness. The oscula are generally simple or slightly 

 elevated, but occasionally they are projected as conical fis- 

 tulse to the extent of nearly half an inch. 



On treating a portion of the sponge with boiUng nitric 

 acid, globular vesicles were separated from the sarcode, 



