Stephens — The Fresh-water Sponges of Ireland. 221 



by sido in lakes and rivovH (ni i ion -calcareous rocks. If only one species is 

 present, that species is almost always Ileteromei/enia Rijderi, whicli is thus the 

 most widely spread as well as the commonest sponge in tiie areas in which it 

 grows. Very rarely three species are found growing together in any lake ur 

 river. On only two or three occasions were the two foregoing species found 

 iu company with a third, wsim&ly,^/^)^ Eiihijdatia fluviatilis. For example, 

 these three species were found together in Lough Nacorra and Moher Lough, 

 in County Mayo. Ejihi/datia fhmiatilis, however, varied in its appearance in 

 these lakes, as it was found one year in abundance, leaving no trace of its 

 presence in the following year. In limestone rivers and lakes Spongilla 

 lacustris and Ejilnjdfdia fluviatilis sometimes occur together, but often only 

 one or the other is present. The remaining species — Spongilla fiufjilis and 

 Uphi/datia Mullcri — are too rare to admit of any general statement about 

 their occurrence. The fact that rarely more than two out of the five species 

 grow side by side at a given spot in Ireland is a contrast apparently to the 

 mode of occurrence of fresh-water sponges in some other parts of Europe. 

 For example, all five species known in France are met with at one spot in 

 the Eiver Saone, close to the fresh-water station recently established in the 

 Cote d'Or (Topsent). 



The same species of sponge may be found year after year in any given 

 lake or river in this country. The only noticeable exception to this appears 

 to be the occurrence of Ephi/datia flxtviatilis in the west of Ireland. This 

 species varied in its appearance from year to year in a couple of lakes in County 

 Mayo in which it had been found (41, p. 3). But it should be noted that 

 Ephi/datia flicviatilis is a rare species in the west, and is evidently not well 

 established there. 



To sum up the distribution of fresh-water sponges in Ireland — Spongilla 

 lacustris occurs tliroughout the country in both limestone and non-limestone 

 areas, both in low-lying lakes and rivers and in mountain tarns and streams. 



Hcteromeyenia Eyderi is only found in the fresh water of non- limestone 

 districts, hence it occurs all round Ireland in the maritime counties which 

 lie off the limestone, and is absent from the central limestone plain. It is 

 commoner in mountain lakes and streams than the preceding species. 



Ephydatia fiuviatilis grows in both limestone and non-limestone areas. 

 It is rare in the west, and has not yet been found in the south-west. It is 

 quite common in the eastern counties from north to south. The species has 

 not been taken in mountain tarns and streams. AVith the exception of 

 Tjough Nacorra, in County Mayo, which lies at 589 feet, it is only kudwn 

 from quite low-lying localities. 



The remaining two species are very rare. Spongilla fragilis has been 



R.I. A. PROC, VOL. SXXV, SECT. B, [2 C] 



