292 A MONOGRAPH OF THE 



The fasciculi of the skeleton has seldom more than two 

 or three spicula bound together, and these are short, not 

 exceeding half the length of those of Halichondria panicea ; 

 but in proportion to their length they are rather stout. A 

 full-sized one measured fisth inch in length. The colour of 

 the three specimens is uniform, a rich nut-brown through- 

 out their whole substance. 



From the variability in its form, and the general paucity 

 of determinable characters, I have designated this species 

 indistincta. 



12. IsoDiCTTA DENSA, Bowerbank. 



Sponge. Massive, sessile, or parasitical; surface uneven, 

 but smooth. Oscula simple, or slightly elevated, dis- 

 persed. Pores inconspicuous. Dermal membrane 

 pellucid, furnished with a unispiculate dermal net- 

 work ; spicula same as those of the skeleton. Skeleton. 

 Rigid and strong ; primary lines bi or trispiculous ; 

 spicula fusiformi-acerate, stout, and short. 



Colour. — Light brown. 



Habitat. — ^Polperro, Cornwall, Rev. A. M. Norman. 



Examined. — In the dried state. 



I am indebted to my kind and indefatigable friend, the 

 Rev. A. M. Norman, for my knowledge of this species. He 

 sent me four specimens for examination, all of which were 

 collected at Polperro. None of them exceeded two 

 inches in diameter, and a thickness of about four lines. 

 The bases of three of the specimens exhibit evidence of 

 only partial attachments to a flat surface, and the fourth 

 was parasitical on a Sertularian Zoophyte, the branches of 

 which pass out through several parts of its surface. The 

 structural characters of the sponge are few and simple, but 

 they are at the same time distinct and striking, 



There is a close structural resemblance between this 

 species and Isodidya indistincta, but the spicula of the 



