1872.] DR. J. S. BOWERBANK ON THE SPONGIADJE. 121 



with their radii minutely and entirely spinous ; they appear to be 

 evenly dispersed on all parts of the deeply seated membranes. The 

 strongly marked character of these spicula, combined with those of 

 the dermal membrane, renders the retentive spicula of this sponge the 

 most descriminative of all its specific characters. 



I found but one instance of external gemmulation, that represented 

 by fig. 12 (Plate V.) illustrating this paper. 



Tethea norvagica, Bowerbank. 



Sponge spherical, sessile. Surface papulous, even. Oscula and 

 pores inconspicuous. Dermis thin and pellucid, furnished abun- 

 dantly with minute subsphero-stellate spicula ; radii conical, acute. 

 Skeleton — radii abundantly spiculous, compact in the interior, ra- 

 diating at their distal extremities ; spicula fusiformi-acuate. Inter- 

 stitial membranes — tension-spicula fusiformi-acuate, long and slender, 

 very few in number ; retentive spicula minute, subsphero-stellate, 

 very abundant, and a very few large spicula of the same form near the 

 dermal surface. 



Colour light green, preserved in saturated salt and water. 

 Hah. From Drontheim to North Cape, from 20 to 200 fathoms 

 {Mr. M' Andrew, 1855). 



Examined in the condition in which it came from the sea. 



I am indebted to the kindness and liberality of my friend Robert 

 M'Andrew, Esq., for thirty-seven specimens of this interesting sponge. 

 They range in size from 2 to 7 lines in diameter. Their substance 

 is very firm, and they vary little from the regular spherical form. 

 The general aspect of the surface is even to the sight and touch ; 

 but it is in truth formed of numerous flat-topped papillae, each de- 

 riving its form from the radiation of the distal end of one of the 

 stout skeleton-fasciculi, the terminal spicula of which are corym- 

 bose ; and the whole of the terminations appear amenable to the 

 same law. The inhalant pores are situated in deep depressions 

 between the terminal papillae ; and immediately beneath them there 

 are large and often tortuous intermarginal cavities. The dermal 

 membrane is profusely furnished with the minute subsphero-stel- 

 late spicula ; and this abundance of the spicula also obtains in the 

 lining membranes of the intermarginal cavities ; but beyond these 

 parts the minute stellate spicula are distributed much more sparsely. 

 Within this region of abundance there is also a dense accumulation 

 of the sarcode, firmly cementing the distal terminations of the ske- 

 leton-fasciculi together, so as to form a stout dermal rind of compa- 

 ratively considerable thickness. Within this thickened portion of 

 the surface of the sponge a very few subsphero-stellate spicula of 

 large size were found ; but none of them could be detected among 

 the deeply seated interstitial membranes. I could not detect the 

 oscula in any of the specimens in my possession. 



The skeleton-fasciculi radiate from the centre of the sponge ; 

 and the spicula composing them have all their hemispherical bases 

 directed to that point. They are closely and firmly cemented toge- 



