PLATE LXXII. 189 



HYMENIACIDON PLACENTDLA, Bowerbank. 

 Plate LXXII. 



Sponge compressed, flat, sessile. Surface smooth. 

 Oscula simple, depressed. Pores inconspicuous. Der- 

 mis smooth, abundantly spiculous ; tension spicula 

 large, acerate, same as those of the skeleton, and 

 large equi-angulated attenuato-triradiate, radii fre- 

 quently distorted, few in number ; also sub-inflato 

 acerate, incipiently-tuberculated, dispersed, minute, 

 and very numerous. Retentive spicula, attenuato- 

 elongo- stellate, very minute and numerous. Skeleton 

 diffused, spicula sub-fasciculated, acerate, rarely 

 acuate, large and long. Interstitial membranes pel- 

 lucid ; tension spicula sub-inflato-acerate, incipiently- 

 tuberculated, very numerous. Retentive spicula 

 attenuato-elongo-stellate, very minute and numerous. 



Colour. In the dried state, cream white. 



Habitat. The Hebrides, J. G. Jeffreys, Esq. 



Examined. In the dried state. 



I am indebted to my friend Mr. J. G. Jeffreys for 

 two specimens of this sponge. They are in form like 

 an irregularly made biscuit-cake; each of them from 

 three to five lines in thickness ; one of them is four 

 and a half inches long by three in breadth, and the 

 other, two inches long by one and a quarter broad. 

 The edges are more or less thick and obtuse. I could 

 not detect a basal attachment on either of them. 

 The oscula on the larger specimen are abundant on 

 one of the two broad surfaces, while very few are 

 apparent on the other one ; they are numerous and 

 very equally dispersed, and vary from half a line to 

 about a line in diameter. On some parts of the 

 same surface the pores are visible by the aid of a lens 

 of two inches focus. The dermal membrane is 

 thin and very pellucid and is crowded with its 

 various spicula. A few, comparatively, of the large 

 skeleton spicula are embedded on its under sur- 



