Stkphrns — The Frexh-ivntcr Sponf/ra nf TrelaiuJ. 207 



in 1881 (14), and Potts'- important ninnnrria])!! in 1887 (33). It would be 

 impossible to enumerate in this short snrvey even all the more important 

 papers on the fresii-watcr sponges pnlilislied about this period, but a complete 

 and valuable list of the literature on the subject up to the year 1892 is given 

 by Weltner (51). 



During the last thirty years much work has been done on the structure, 

 physiology, and dexelopmcnt of the Spongillidae, while scientific exploration 

 carried on during recent years in many parts of the globe has proved that 

 fresh-water sponges may be found under suitable conditions throughout the 

 world, and new species are being continually added to the number already 

 known. 



Fresh-watek Sponges in Ireland. 



Although the fact tliat fresh-water sponges occur in Ir-eland has been 

 known for just one hundred years, and although systematic search has 

 recently been made for them in many different parts of the country, only five 

 species have so far been found. They are as follows : — Spongilla {Euspomjilla) 

 lacustris auct., Spongilla {Eiinctpius) fragilis Leidy, Ephydatia Jluviatilis 

 auct., Ephydcdia MiUlcri Lieberkiihn, and H deromeyenia Ryderi Potts. 



Key to the Irish Spongillidae. 

 I. Genimule-spicules rod-like (strongyla or oxea). Genus Spongilla. 



1. Skeleton-spicules, smooth oxea; free mieroscleres present. 



Gemmules occurring singly, and provided with a 

 pneumatic-coat of very minute cells (sub-genus Euspon- 

 gilla). No foraminal tubule. Spongilla lacustris. 



2. Skeleton-spicules, smooth oxea ; no free mieroscleres. Gemmules 



in a pavement-layer at base of sponge, and in small scattered 

 groups, enclosed in both cases in a common covering of 

 large polygonal cells (sub-genus Eunapius). Foraminal 

 tubule present. Spongilla fragilis. 



II. Gemmule-spicules amphidiscs of one kind, with equal discs which are 

 serrated at the edge. Genus Ephydatia. 



1. Skeleton-spicules typically smooth, but some microspined. 



Shaft of amphidlsc longer than the diameter of the disc; 

 disc not deeply serrated. Bubble-cells absent. Ephydatia 

 fluviatilis. 



2. Skeleton-spicules smooth and spined. Shaft of aniphidisc 



shorter than the diameter of the disc ; disc deeply serrated. 

 P.ubble-cells present. Ephydatia Miilleri. 



[2 8 2} 



