1863.] DR. J. S. BOWERBANK ON THE SPONGILLIDiE. 445 



our knowledge, and indicates a very extensive range for the genus. 

 And not the least remarkable point in its history is its very close 

 approximation in habit and structure to our British species <S. flu- 

 viatilis. During my examination of the Australian specimen, I met 

 with two spicula of the same form, entirely spined, cylindrical, which 

 do not belong to S. Capewelli, and which are probably tension-spi- 

 cula, or spicula of the ovaria, of a second species existing in Lake 

 Hindmarsh. 



Spongilla FLUviATiLis, Johuston. 



Sponge massive, sessile ; surface uneven, often lobular, hispid. 

 Oscula simple, large, scattered. Pores conspicuous. Dermal mem- 

 brane pellucid, aspiculous. Skeleton-spicula acerate. Ovaria sub- 

 globose ; spicula birotulate, short, rarely spinous ; disposed in lines 

 radiating from the centre of the ovarium ; rotulse equal in size, flat, 

 deeply and irregularly dentate, diameter equal to the length of the 

 shaft of the spiculum. 



Colour, alive, yellow or green. 



Hab. Rivers and lakes of Europe, 



Examined alive. 



Dr. Johnston, in his * History of British Sponges,' has 'given so 

 able a digest of all that has been written regarding this species and 

 its numerous changes of name, both generic and specific, as to render 

 any observations on that part of my subject a work of supererogation. 



The normal form of this species is certainly massive and sessile ; 

 and the arborescent form that it is said to occasionally assume is due 

 to its having originally been parasitical on stems of plants, and per- 

 haps also not unfrequently to S. lacustris having been mistaken for 

 this species. When developed under favourable circumstances, I have 

 seen large rounded lobes projected from its surface ; but I have never 

 seen it assume an arborescent form like that of S. lacustris. 



The absence of spicula in the dermal membrane of this species 

 readily distinguishes it from S. lacustris ; but the most striking dif- 

 ferential character exists in the birotulate spicula of the ovaria, the 

 correct form and position of which were, I believe, first pointed out 

 by Meyen in Valentin's 'Repertorium,' 1840. 



The shaft of the spiculum is usually smallest at the middle, and it 

 increases more or less as it approaches the rotulse ; and occasionally, 

 but rarely, we find a single large spine projecting at right angles 

 from near its middle. The rotulse are flat and deeply and irregularly 

 divided, the divisions frequently extending from the circumference to 

 very near the centre. They are disposed very closely together in 

 the walls of the ovaria, the outer rotula supporting the external 

 membrane, and the inner one performing the same office for the in- 

 ternal membrane ; but they are so completely covered by the re- 

 spective membranes, that without the application of nitric acid they 

 would be extremely likely to escape observation. 



Spongilla Lkidii, Bowerbank. 



Sponge sessile, coating thin ; surface tuberculated, minutely hispid. 



