62 A MONOGRAPH OF THE 



tures, at first led me to expect that it was a complete 

 specimen of P. ornatus, but the characters of the spicula 

 quickly dissipated that illusion. The delicacy and thin 

 condition of the structures of the fistula very closely 

 assimilate them with those of P. ornatus, but while the 

 latter has the external defensive spicula acuate, those of 

 P. bulbosa are decidedly spinulate. 



3. Polymastia robusta, Bowerbank. 



Sponge. Sessile, coating; surface even, smooth. Oscnla 

 terminal, congregated on numerous stout, long, 

 mammaeforui, cloacal fistulas ; apices of fistula? ob- 

 tusely conical. Pores inconspicuous. Dermis coria- 

 ceous, armed abundantly with stout, ensiform spinulate 

 spicula. Skeleton. Spicula super fusiformi-acuate, 

 large and long. Interstitial membranes stout, com- 

 pound, formed of layers of fibro-membranous tissue ; 

 fibres parallel, layers disposed most frequently at right 

 angles to primary skeleton fasciculi, occasionally 

 diagonally to them. Tension spicula acerate, very 

 minute, rather few in number. 



Colour. Alive and dried, fawn-yellow. 



Habitat. Coast of Northumberland, Professor Win. 

 King, of Galway; three miles off Dunstanborough, 

 Northumberland, Rev. A. M. Norman. 



Examined. In the dried state. 



The best specimen I have seen of this fine species was 

 presented to me by my friend, Professor King, of Queen's 

 College, Galway. He informed me it was brought up by 

 hook and line, in about 40 fathoms of water, about 40 

 miles from the Northumberland coast. 



The sponge coats a surface of about nine square inches, 

 and has thirty-nine of the tubular mammaetbrm fistuhe 

 upon it, many of them exceeding an inch in length, but on 



