208 Proceedings of the Rotjal Irish Academy. 



III. Gemmule-spieules amphidises of two kinds. Genus Heteromeijenia. 



1. Skeleton-spicules densely spined. Genininle-spieules (a) 

 long-shafted amphidises, the disc formed of several strong, 

 recurved teeth united at the hase ; (h) short-shafted 

 amphidises, with finely serrated edges to the discs. 

 Heteromeyenia lli/dcri. 



Although the numl>er of sjjecies is small, yet the fresh-water sponge-fauna 

 of Ireland compares favourably with that of the conntries lying nearest to 

 her. England and Scotland together possess the same species. France has 

 the fulliiwing five : Spongilla lacustris, H. fragilis, Kphydatia JluviatUis, 

 E. Mulleri, and Trochospongilla Jiorrida. Six species occur in Germany, 

 namely, the five that are found in France, witli the addition of Cartcrhis 

 Stepanotci. Only about eight species are known to occur in the whole of 

 Europe. One of these, Utteimncyaiia Ryderi, as far as its European distri- 

 bution is concerned, is limited to the extreme western outposts of the 

 continent, while the gemmules only of another North American species, 

 lleteromeytnia re/>ms, have on one occasion been found in Europe, namely, in 

 a pond in Galicia. Several species of doubtful value have been described 

 from time to time ; but the following are generally recognized as comprising 

 the fresh-water sponge-fauna of Europe: — 



S,t,,nffilla lacustris. Jleleromtyenia liyderi. 



■filla fratfUis. Hcteromeymia repcn<i. 



Kphydatia flurintUis. Trochosjiongilla horrid/i. 



Kphyd'itiii iliJlrri. Cartfriim Stejmnoun. 



Thus Euiojio is p<M)r in nuuiln-r of species a.«i compared with other parts of 

 the wtirhl. At the pi-esent time North America is known to possess about 

 twenty-eight 8iK?cie.<», the Aniazun region of South America about twenty, 

 the Continent of Africa over thirty, and India, including I'.urma, at least 

 twenty-fivt' - md .several varieties. 



The geu^ -i : . >i distribution of the fresh-water sjionges found in Iieland 

 is wide. JIfteromryenia Ilydtri has the most restricted range, being known 

 up to the present only from Nortli America, Ireland, and Scotland. Tlie 

 remaining sjiecies occur lliroughout the entire Holarctic region. E. Sliilleri 

 api)ears to W confined to tlial region, where it extends through North America, 

 Europe, and Northern Asia to Japan. S. lantstris, S. frayHis, and E. fltivia- 

 tUis are represente«l by at least local races or varieties in other parts of llie 

 world. Thus S. IntuMris is re[>resented in India. S./rayilis occuis in South 

 America, tropical Asia, and Australia, wliile forms of E. fliitialilis are found 

 in tropical Asia, South Africa, and Australia. 



