302 A MONOGRAPH OF THE 



The skeleton spicula are rather slender in their pro- 

 portions ; one of the largest and best developed specimens 

 measured T ^th inch in length. 



The length of the spicula of this sponge is very nearly 

 the same as that of I. pallida, cinerea and indistinct a, but 

 it may be readily distinguished from these species by its 

 external characters, and especially so by its prominent 

 hispidation. 



I have dedicated this species to the Rev. Walter Gregor, 

 late of Macduff, now of Aberdeen, an able and ardent 

 working naturalist, to whom I am indebted for the use of 

 many interesting northern species during the progress of 

 my work. 



19. IsoDien'A fallax, Bowerbank. 



Sponge. Massive, sessile. Surface even, smooth; fur- 

 nished irregularly with fistnlar projections, variable in 

 size and form; parietes thin. Oscula terminating 

 large fistulas. Pores conspicuous, numerous. Der- 

 mal membrane thin and pellucid, furnished with a 

 unispicular network, smooth ; spicula same as those 

 of the skeleton ; tension spicula acerate, very slender, 

 few in number; and tricurvate acerate, minute and 

 very slender, rather numerous. Skeleton. Diffuse 

 and very irregular ; primary and secondary lines 

 scarcely to be distinguished, mostly unispiculous ; 

 spicula acerate, rather long. Interstitial membranes. 

 Tension spicula same as those of the dermal mem- 

 branes. 



Colour. Dried, light gray. 



Habitat. Off Saints' Bay, Guernsey, Rev. A. M. 

 Norman. 



Examined. In the dried state. 



1 received the specimen described above, in company 



