Stki'Hi;ns — The Fresh-tvater Sponges of Ireland. 231 



typical oxea measure between U'24 and 047 nun. in lengLli. They du not vary 

 so much as this m a single specimen. Their most usual length is hetween 0"25 

 and 0"37 mm. Their maximum diameter is usually O'Olo mm.; but it varies 

 from O'OOS to 0'015 mm. in difTerent specimens. The shorter, thicker megas- 

 cleres present iu many specimens are, as a rule, between 0'22-0"26 mm. in 

 length, and have a maximum diameter of 0'02 mm. 



The gemmule-spicules of E. fluviatilis vary also to some extent. In tlie 

 more typical specimens of the species the shaft of the amphidisc is smooth, 

 or is so minutely spined that it looks merely roughened ; or it may have one 

 to several long, sharp spines projecting from it. The disc is indented ; it is 

 either divided into a number of fairly even, small teeth, or it is cut by 

 several deeper indentations into broader sections, the outer edges of which 

 are toothed. The teeth themselves may be very finely spined. In speci- 

 mens which are not so robust in growth, and which possess rather slender 

 megascleres, the amphidiscs are slender also, and there is more tendency for 

 them to develop irregularities such as have been described and figured from 

 time to time by various writers ; for example, by Wierzejski (56), which 

 writer notes in passing that the skeleton-spicules are slender in the speci- 

 mens examined by him possessing irregularly shaped amphidiscs. The shaft, 

 for instance, may be thickly covered with long spines, and may project as a 

 sharp point beyond one or both discs. The discs themselves may be variously 

 developed, and may often be merely an irregular bunch of strong spines 

 projecting from the thickened ends of the shaft, or they may be reduced to 

 one or two strong spines projecting at various angles, so that the spicule 

 assumes an irregularly star- shaped form. 



The amphidiscs are 0-025-0*027 mm. in length, and the diameter of the 

 disc is 0-015-0-02 mm. 



Localities. 



WATteRFORD. — Bally L. to the north of Dunmore. 



TiPPERARY, — E. Suir at Kilsheelan, Anner K. 



Kilkenny. — E. Barrow at Graiguenamanagh. 



Wexford. — E. Bann near Oamolin. 



Caulow. — E. Barrow near Tinnahinch. 



Galway.— L. Corrib near Oughterard, Coole L. (coll. E, A. Phillips). 



King's Co. — Lake in Birr Castle Demesne (coll. U. A. Phillips). 



Kildaue. — E. Barrow at Mageney (34), Eye Water, at Leixlip. 



Dublin.— E. Liftey, U. Dodder, Eaheny ponds (21), stream at Edmonds- 

 town, Grand Canal, Eoyal Canal, E. Tolka, pond at Crumlin, pond in 

 Zoological Gardens. 



