230 PROCEEDINGS OF THE ACADEMY OF [1887. 



small portion of the Brandywine, narrows into the forebay and hur- 

 ries on to the clattering wheels. At this point a rock-built over- 

 flow, like a dam breast, had checked a number of nearly water-log- 

 ged timbers, and others were aground in the shallow water below. 

 Many of these when turned over disclosed specimens of a filmy gray 

 sponge, branching off here and there along the surface of the wood, 

 yet with a curious want of continuity, as if its particles, in their haste 

 to march forward, had neglected to keep open communication with 

 their base of supplies. All along the lines and dotting the broader 

 portions, small white or yellowish gemmules gleamed through the 

 thin dermis, instead of being buried as in most other sponges in the 

 deeper parts of the tissues. 



This was the first discovery of M. crateriformis ; it was afterward 

 found in somewhat similar situations and with like characteristics 

 in several other Pennsylvanian streams. So far as I remember, 

 none of this species has reached me from abroad, except in one in- 

 stance, where the situation and circumstances were entirely dissim- 

 ilar. They will be found described in association with the sketch of 

 Meyenia phimosa. 



M. crateriformis was far from being the only sponge found on the 

 occasion above described. In the lower corner of each mill, where 

 the water boiled and rushed as it escaped from under the wheels, 

 the stones and timbers bore many specimens of S. lacustris, S. fra- 

 gilis and 31. fiuviatiUs, The growth of the second of these, upon 

 timl)ers lining the inner walls of the grist mill, Avas particularly 

 abundant, nearly white and full of segregated spores. 

 (16j Meyenia everetti, Mills. Proc. Am. Soc. Micros. 1884. (PL X, fig. iii, and iv.) 



Sponge green, without sessile portion, but consisting altogether of 

 slender meandering filaments, little more than a sixteenth of an 

 inch in diameter ; made up of central lines of closely fasciculated 

 skeleton spicules, with short thin lines of the same, diverging at an- 

 gles of 30 to 50 degrees, and, on the surface, numerous single spic- 

 ules, as yet unplaced, and forming no proper network. Near their 

 ends the fronds were abruptly reduced, nearly to the diameter of the 

 central band of spicules, and appeared to terminate in a sharp 

 point. 



Gemmules few but unusually large, as the crust is thick and the 

 embedded birotulates are longer than in most other species. They 

 are found axially, in a single series, along the fronds ; each enclosed 

 in a rather loosely formed capsule or cage of skeleton spicules, the 



