308 A MONOGRAPH OF THE 



off Hastings, in the spring of 1803, parasitical on a Sertu- 

 laria. It agrees very closely with the type specimen in all 

 its essential characters. 



23. Isodictya simulans, Boiverbank. 



Halichondria simulans, Johnston. 



Sponge. Sessile, simply branching, or irregularly latticed 

 by cylindrical inosculating branches, or polymorphous. 

 Surface smooth. Oscula simple or slightly elevated, 

 frequently at nearly regular intervals on one side of 

 the branch. Dermis furnished with a strong irregular 

 reticulation of single spicula ; spicula acerate, same 

 size as those of the skeleton ; dermal membrane pel- 

 lucid, aspiculous. Skeleton. Compact and stout, 

 rather irregular ; primary lines multispiculous ; secon- 

 dary lines rarely more than unispiculous, numerous, 

 and irregularly disposed ; spicula acerate, short and 

 stout. Interstitial spaces large and irregular ; mem- 

 branes nearly obsolete, aspiculous. 



Colour. Dull green or dusky brown. 



Habitat. " Connemara, Win. M. Colla; Dublin Bay, 

 Dr. A. H. Hassall." Brighton, Mr. Thos. Ingall ; Tenby 

 and Diamond Ground, off Hastings, J. S. Bowerbank. 



Examined. In the dried state. 



In its full state of development this sponge has as com- 

 plex a latticed form of its branches as the best developed 

 specimens of Clialina Montaguii, but it is more frequently 

 found in the form described and figured in Dr. Johnston's 

 1 History of British Sponges,' plate viii, figs. 1 and 2, p. 109. 



In the fresh state this species is strong and rigid, and 

 when dried, hard and brittle. In its simplest branching 

 form, the oscula are frequently disposed on one side of the 

 branch, and at nearly equal distances from each other, and 



