188 PROCEEDINGS OF THE ACADEMY OF [1887. 



Gemmule spicules generally cylindrical, much and variably curved; 

 somewhat sparsely spined ; spines more numerous near the extrem- 

 ities, where they are long, acute, and frequently recurved. Upon 

 the gemmules they vary from a horizontal to a nearly erect position, 

 according to the thickness of the crust, and for the same reason 

 are sometimes wanting and at others very numerous. 



Hah. On stones and timbers everywhere; preferring running 

 water. 



Measurements. Diameter of gemmules 0.02 inches. Average 

 length of skeleton spicules about 0.0108 inches. 



Remarks. Spongilla lacustris is certainly not introduced in 

 this connection on account of any claims I desire to make as to au- 

 thorship or discovery ; but rather in the way of recantation or con- 

 fession that in times past I have so frequently mistaken this name- 

 child of the great Linnseus, clucking to it as one of my own little brood. 

 Indeed it is to save others from a similar experience that I am par- 

 ticular to make this identification. 



This species was one of the earliest known ; though for years the 

 distinction between it and SpongiUa (now Meyenia,) fiuviatilis was 

 far from clear. It has been found in nearly all parts of the world 

 where any sponges have been discovered. AVhile many of the fresh 

 water sponges appear to shun the light S. lacnstris comes out boldly 

 and flourishes in the full sunshine. For this reason and because of 

 its resultant brilliant green color and its conspicuous branching- 

 habit, this sponge is better known than any other, and is more fre- 

 quently gathered by the non-expert collector. I have received it 

 from nearly all my correspondents in the United States and from 

 almost every locality in Avhich any have been collected. 



In every place it prefers rajiidly running water, where its growth 

 is strong and vigorous. Perhaps my finest specimens were gathered 

 .at a place in Chester Creek, Pennsylvania, where the stream was 

 narrowed to a width of ten or twelve feet, rushinsr between large 

 imasses of rock, many of which w^ere coated with the sessile sponge 

 and beautifully fringed with tapering finger-like processes, one half 

 inch or more in diameter by several inches in length. In standing- 

 pools, on the contrary, it grows in slender cylindrical branches; as 

 in the subsiding reservoirs on Fairmount Hill, Philadelpliia, where 

 it appears in slender, flaccid, yellow-green branches, with hardly 



