222 Proceedings of the Royal Irish Academy. 



taken in five widely separated localities, lying in the extreme north and sonth 

 and in the west and north-west, while liphydatia Mi/Ueri has only been found 

 80 far in the Eiver Erne, at Enniskillen ; the Paver Tolka, in County Dublin; 

 and in Caragli Lake, in County Keriy. 



Family SPONGILLIDAE. 

 Spongilla ( Euspone^illa) lacustris auet. (PI. XXVI, figs. 1, 2.) 



Thi.s species is l"« luid all over Ireland, both in limestone and non-limestone 

 districts. It liourishes in lakes and rivers and in the canals, and is the most 

 widely spread species in Ireland, but in the areas where Heteromeyenia Ryderi 

 occurs it is by no means the commonest ; while in some of the eastern 

 counties, in County Dublin for example, it is mucli rarer than Fphi/dntia 

 flitriatilU. 



Like all the fresh-water sponges in Ireland, S. lacvstns usually grows 

 on stones, either on the upper surface, when it is brandling or massive, or on 

 the under surface, when it forms thicker or thinner encrustations. It some- 

 times grows on water-plants, and lias been found on the submerged roots of 

 trees, such as the alder, growing on the banks of rivers, ami on tiie stone- 

 work of canal locks. Branching specimens, which are so typical of the species, 

 are of much rarer occurrence in Ireland than encrusting ones. 



As is usually the case with fresh-water sponges, S. lacKstris is bright green 

 when growing exposed to the light; when sheltered from the light it is 

 greyish-white or pale yellowish. In lakes witli very peaty shores it is 

 sonietimoa a dull purplish-brown colour. An interesting variety of colour 

 was exhibited by specimens growing in great profusion on the pebbly bed of 

 the Iliver Shannon, about half a mile below Lough Allen. Some of the 

 sponges were a fairly bright, though not a vivid, green, but all were tinged 

 more or less with a dark grey colour. Some were of a uniform dark grey 

 externally and a pale yellowish green colour internally. One large specimen 

 was ash-grey in colour, with most of its branches tipped with white, which 

 rendered it very conspicuous even at some little distance. Another branching 

 specimen was in jvirt green, in part coloured similarly to the foregoing. These 

 sponges were loaded with particles of silt brought down from the Coal 

 Measures on which the gi-ealer part of Lough Allen lies. 



S. lacustris is found commonly in mountain lakes and in their out-flowing 

 streams, but it is comparatively rare in the higher mountain tarns, and has 

 only lieen taken at three or four localities lying at an altitude of 1,000 feet or 

 over. It was found in a little tarn at 2,200 feet on Mount Brandon in the 

 Dingle peninsula, and in the stream draining the lake. It was also taken 

 lower down the mountain in the stream draining Lough Nalackcn (1,000 feet). 



