BRITISH SPONGIADjE. 367 



the sponge to which I have allocated the name of Montagu. 

 It is quite possible that the differences in form between the 

 two may arise from the differences in their localities, and in 

 the form and modes of ramification of the Fuci or Zoophytes 

 on which they are usually parasitical. 



My late friend Mr. Thomas Ingall obtained a great num- 

 ber of specimens of this sponge, which were collected at 

 Brighton, and which are now in my possession, and among 

 them there is a very great variety in both size and form. 

 In some the inosculating latticed form is very irregular and 

 open, the cylindrical branches not exceeding two or three 

 lines in diameter, and the whole sponge has a fragile and 

 delicate appearance ; while in others, the branches coalescing 

 by juxtaposition, or increasing in diameter by age, assume 

 a compressed or very irregularly cylindrical form, and attain 

 a diameter of nearly or quite half an inch, and the inter- 

 vening spaces becoming less in width. In this condition 

 the sponge very closely resembles the large and complex 

 specimens of Isodictya simulans when dried, but from which 

 they may be readily discriminated by their softness and 

 elasticity. 



The irregular latticed and inosculating character of this 

 sponge is greatly dependent for its form to the Fucus or 

 Zoophyte on which it is parasitical. It appears to com- 

 pletely envelop and foUow the direction of the body on 

 which it is developed, and the branches appear to inosculate 

 whenever they happen to touch each other ; and it is only 

 when they outgrow the base on which they were first 

 formed, that they continue their course as cylindrical 

 branches independent of extraneous support ; and they 

 then frequently have a wide terminal oscular orifice. 



The tubes generally extend through the whole length of 

 the branches, but not with an equable diameter, and their 

 parietes have no oscular membranes ; they do not, there- 

 fore, appear to be regular cloacal fistulae, but rather to ex- 

 hibit a greater proportional development of the system of 

 excurrent canals than is usual in ramose sponges ; the oscula 

 are frequently small and simple, and are found dispersed on 

 all parts of the branches ; at other times they are large and 



