No. 1.] G. M. DAWSON— CANADIAN SPONGILLA. O 



The spongilla is sessile, and branches much, well-grown speci 

 mens much resembling fully developed examples of S lacustris. 



Length of skeleton-spicula 0.013. Dermal and interstitial 

 spicula, 0.0015 to 0.0017 inch. 



Fig. 3. — a, ordinary skeleton-spiculum. A. and B., ordinary 

 capsular and dermal spicula. 



Spongilla stagnalis, sp. nov. Sponge encrusting, forming 

 patches several inches in diameter, and from half an inch to an 

 inch thick; greenish; lobular, somewhat hispid. Oscula simple, 

 key-hole shaped, or double ; large, 0/25 to 0.50 in. Scattered, 

 sub-crateriform. Skeleton-spicula acerate and fusiformi-acerate, 

 slightly arcuate, 0.011 to 0.013 in. long. Most of the stouter 

 spicula medially spined, the apices always naked ; spines small, 

 sparsely distributed. Ovaria, sub-globose, diameter, 0.025 in. 

 Rotulae, about equal in size, flat, very deeply and irregularly 

 dentate, diameter about equal to length of shaft of spiculum, or 

 0.0005 in. ; the rays not acute. Shaft, thick, cylindrical, gener- 

 ally with a boss at each end. 



Hab. North-west Angle Inlet, Lake of the Woods ; River St. 

 Lawrence near Montreal. 



The two forms of skeleton spicula seem to pass into each 

 other, and in specimens from both localities, are very irregular 

 in size. The birotulate spicula — especially in the Lake of the 

 Woods specimens — are very apt to be deformed. A number of 

 small, entirely spined, straight, obtuse spicula, about one-third 

 the length of the skeleton-spicula, were found with the others ? 

 after treatment with acid. They were searched for in all pirts 

 of the sponge, but finally found enclosed in some of the gem- 

 mules, and apparently in connection with the young sponge. 



This species, which is nearest the European type S.fluviatilis^ 

 of Johnston, was found in great abundance at the first mentioned 

 locality, in July, 1873. It was growing on floating logs and 

 branches, and many specimens were filled with large gemmules. 

 It is probably the species the existence of which was suspected 

 by Dr. Bowerbank, who says, in the conclusion of his notice of 

 S. Dawsoni : — " In the preparation of these spicula for examina- 

 tion, I found a few birotulate ones, having the rotulas very 

 deeply divided. These spicula were no part of the sponge in 

 course of description, but were undoubtedly from the gemmules 

 of another species inhabiting the St. Lawrence. " 



