W. B. PRIEST ON SPOXGILLA FRAGILIS. 253 



ous layer. Oscula simple, dispersed, pores inconspicuous. 

 Colour light brown to green. Skeleton spicule, acerate, some- 

 times curved, fusiform, gradually sharp-pointed, smooth and 

 sometimes inflated in the centre. Statoblasts somewhat bottle- 

 shaped, congregated on the basal membrane beneath the sponge, 

 with the aperture upwards, chitinous coat hemispheroidal, 

 aperture prolonged by a short tubular extension, the chitinous 

 coat being of a dark amber colour, covered by a thin granular 

 crust, with small curved or fusiform cylindrical, entirely spined 

 spicules, the basal membrane abundantly sjriniferous and of the 

 same form as those covering the statoblasts, those on the stato- 

 blasts being arranged more or less tangentially. 



Now for the subject of this communication. Up to the 

 present time only two species of fresh-water Sponges have been 

 recognised in England, viz., Meyenia fiuviatilis and Spongilla 

 lacustris, the former having the crust of its statoblasts charged 

 with birotulate spicules, one end resting on the chitinous coat 

 and the other protruding more or less on the surface, the other 

 species having curved, minute, stout, fusiform, spined spicules 

 arranged tangentially on the statoblasts. Of course we have 

 several so-called varieties of the same, which to my mind are 

 only caused by the variations of surrounding circumstances, 

 such as the slow or rapid flow of the water, with the different 

 amount of light and shade, accompanied by changes of tempera- 

 ture, all of which conditions must influence the development 

 and colour of the Sponges to a great degree. 



On the fourth of September of last year I went to Shepper- 

 ton, walking over to Walton-on-Thames, and in one of the back 

 waters, called, I am told, Walton Sale, growing on the sub- 

 merged roots and branches of the willow trees overhanging the 

 stream, I collected a quantity of very good typical specimens of 

 both species. On examining what I had collected the next 

 morning, I discovered about an inch of a branch, on which some 

 Sponge had developed an incrustation, and on examining it 

 under the microscope, it proved to be Spongilla fragilis, one layer 

 of statoblasts partly overlying the other, and partially covered 

 with Meyenia fiuviatilis. It answered exactly to the description 

 I have just now given of that species, also described by Mr. 

 Mills, in having only a very small portion of the Sponge struc- 

 ture remaining, leaving the statoblasts in a more or less con- 



