228 Proceedings of the Royal Irish Academy. 



the commonest species, and indeed the only one found so far in the rivers of 

 that county, the Liffey, Dodder, and Tolka, with the exception of £]>hi,datia 

 Mulleri, found in the last-named on one occasion ; but it has not yet been 

 recorded for the neighbouring county of Wicklow. It has been found here 

 and there throughout the midlands, where a more detailed search may prove 

 it to be fairly common. 



Like all the fresh-water sponges in Ireland, £. fluriatilis usually grows 

 on stones. It may form thick encrustations or rounded cushion-like masses 

 on the upper surfaces of the stones, or thinner crusts on their lower surfaces. 

 The species is found, but more rarely, on the stems and leaves of water- 

 plants, on the wood-work of the locks of canals, on rotting, submerged 

 branches, or on the living roots of alder trees growing on the banks of 

 rivers. 



The sponge is dark green in colour when exposed to the light, and pale 

 yellowish or greyish when growing in shaded places. In texture it varies 

 considerably ; one specimen may be hard, another quite soft. In the former 

 case the sponge possesses robust skeleton-spicules ; when the texture is very 

 soft the spicules tend to be slender. 



With the exception of its occurrence in Lough Nacorra in Co. ilayo, 

 which lies at an altitude of 589 feet, E. Jluriatilis has been found only in 

 loW'lying lakes and rivers in Ireland. Unlike Spotigilla laauitris and 

 HfifittineiffHiii Hydrri, it has not been found in mountain tanis nor in their 

 outflowing streams. On the continent of Europe it appears also to prefer 

 low-lying localities, but in Asia it has been taken at very high altitudes. In 

 the Kumaon Lakes of the Western Himalayas, for example, it occurs at 

 4,000-6,400 feet (9), and in Issyk-Kul I^ke in TurkesUn at 5.300 feet (55). 



As a rule, E. JluriatUis is vigorous in its growth, with well-developed 

 skeleton- 6 bres and robust spicules, but in situatious where the conditions 

 would appear to be unfavourable it has been found of very small size, with 

 very slender spicules loosely united into poorly developed, weak fibres. In 

 several lakes in the west of Ireland, where the species does not appear to be 

 well established, the sponge, although growing in considerable quantities, 

 possessed very slender spicules. 



Green and actively growing specimens crowded with genimules have been 

 found throughout the year. Gemmules are apparently produced in far 

 greater numbers in this species than in any other of the fresh-water sponges 

 growing in Ireland, with the probable exception of E. JIulUii. 



The skeleton-spicules of E.fluriatUis varj' more than is perhaps generally 

 rec<">u'nized, both in a single specimen and from one 8i)ecimen to another. 

 When it is stated that they var)* considerably, that, for instance, spined as 



