BRITISH SPONGIADiE. 331 



surface at one portion of the sponge, but there is nothing 

 in its appearance to distinguish it from a portion of the in- 

 terstitial membranes, which have slender fusiformi-acuate 

 spicula, and are still more sparingly furnished with small 

 dentato-palmate inequi-anchorate spicula. The destruction 

 of the dermal membranes and the expanded character of 

 the interstitial spaces renders it impossible to determine 

 with certainty, in this specimen, either the position or size 

 of the oscula ; but on viewing the sponge by direct light, 

 with a power of 90 linear, they were apparently very little 

 larger than the insterstitial spaces, few in number, and 

 irregularly dispersed. I am indebted to Dr. Clarke for my 

 knowledge of this species, and I have therefore attached 

 his name to it, in acknowledgment of the kind assistance I 

 have at all times received from him, during my investi- 

 gation of the British sponges, and of his zeal in the pursuit 

 of Marine Natural History. 



39. Isodictta gracilis, Boiverbank. 



Sponge. Ramose, pedicelled ; branches slender, dividing 

 dichotomously or trichotomously, terminations at- 

 tenuated. Surface even ; minutely hispid. Oscula 

 inconspicuous, simple, dispersed, minute. Pores in- 

 conspicuous. Dermal membrane pellucid, aspiculous. 

 Skeleton. Primary lines multispiculous ; secondary 

 ones usually unispiculous. Spicula acuate, small, and 

 rather slender. External defensive spicula same as 

 those of the skeleton. Interstitial membranes. Ten- 

 sion spicula acuate, slender, few in number. Reten- 

 tive spicula bidentate equi-anchorate, minute, and 

 very few in number. 



Colour. Alive, pale buff ; dried, cream white. 

 Habitat. Larne Lough, Ireland, Professor Dickie. 

 Examined. In the dried state. 



I am indebted to my friend, Professor Dickie, for my 



