254 W. B. PRIEST ON SPONGILliA FRAGILIS. 



tinuous layer, the species being infested with innumerable 

 enemies, which devour the sarcode and other living portions 

 of the sponge. 



Now the question is, whether Spongilla fragilis is to be 

 accounted a British Species, or has it simply got into the Thames 

 by accident ? I do not profess that the sponge is entirely new 

 to England, as it was found, for the first time in 1884, by Mr. 

 Stewart Ridley, of the British Museum, in the River Wye. Per- 

 haps, as we, as a nation, are becoming very much Americanised, 

 the Wye and the Thames have caught the infection. At any 

 rate, it has now been found in two of our rivers, and I am in- 

 clined to the belief that other species will be found if sought 

 for, from the fact that a number of fresh-water deposits contain- 

 ing sponge spicules have been met with, belonging to species as 

 yet undescribed, and noticed even as far back as Ehrenberg's 

 time. 



No record of Spongilla fragilis being found in the Thames 

 until now, I thought this communication would be appreciated 

 by those members of the Club who are interested, like myself, 

 in sponge lore. 



Perhaps I may mention that since writing this communica- 

 tion I have received some more Fresh-water sponges from Mr. 

 Thomas, of Chicago, and he calls my attention to one packet 

 containing Spongilla fragilis, in which the statoblasts are 

 more or less in a compound or grouped state. On examining 

 the Thames specimen I found several statoblasts in that condi- 

 tion. 



Explanation of Plate XV. 



Fig. 1. Statoblasts of Spongilla fragilis as they appear in situ. 

 Fig. 2. A Statoblast isolated from the mass showing the flask-like 

 shape. 



Fig. 3. Spicule of statoblast and basal membrane. 



Fig. 4. Skeleton spicule. 



Fig. 5. The grouped or compound form of statoblasts. 



