234 Proceedings of the Royal Irish A cademy. 



specimens the maximum diameter is 0'015 mm., but in others it is 002 mm., 

 or even as much as 0027 mm. The spicules are thus decidedly shorter and 

 thicker than the typical oxea of E. fluviatilis, but more nearly resemble the 

 short, thick spicules often to be found in that species. 



The specimens from the Drumclitt' Kiver and the Eiver Boyle, already 

 alluded to as afTording a clue to the identity of these sponges, are exactly 

 similar to them in external appearance, being hard to the touch, and growing 

 in thin, more or less circular, patches. "With regard to the spicules, the 

 Drumclifif River sponges possess many short, thick, abruptly pointed, smooth, 

 or microspined oxea, and in addition longer, more slender, gi-adually pointed 

 smooth oxea, some of which jx)ssess a central swelling. Tliese latter are like 

 the oxea of typical specimens, which often, it must be remembered, also 

 possess many short, thick spicules, some of them microspined. The sponges 

 possess in addition a few scattered auiphidiscs, which are quite the typical 

 E. fluriatUis shape. The specimens from the Eiver Boyle closely resemble 

 the Drnmclifl' Eiver examples, and, like them, possess scattered amphidiscs. 

 Typical specimens of E. fluviatUU wei-e absent from botli these localities, so 

 that the amphidiscs must belong to the specimens in which they were found, 

 and are not a chance admixture, as so often happens. 



Sponges were collecled in tlie lakes drained by these rivere, in Glencar 

 Lough and in Oakport I/)ugh respectively, which possessed rather short, 

 thick spicules, williout tlie longer ones found in the river specimens (compare 

 the change in the mega-scleres of Ileleromcyenia liydtn under similar 

 conditions), nor were any amphidiscs found even after prolonged searching. 

 With regard to the presence of gemmule-spicules in lake and river sponges, 

 it is interesting to quote Dr. Annandale's reference to the production or non- 

 production of gemmules. He states (6, p. 74) that " evidence, moreover, is 

 accumulating that the adoption of a limnic as distinct from a lluviatile mode 

 of life is liable to produce degeneration of the gemmules in fresh-water 

 sponges." The most notable instance so far known is Hdrromcyenia liyderi, 

 which, Iwth in North America and in Ireland, produces gemmules with great 

 rarity in lakes, and in great abundance in rivers. 



To return to the consideration of the megascleres of the foregoing 

 sponges, if it were imagined that spicules, such as those figured on PI. XXVI, 

 figs. 9, b, c, were pnxluced to the exclusion of the other typos of spicules, the 

 result would be a sponge possessing spicules similar to tlKwc from Ballyscanlan 

 and OakiKtrt Loughs (I'l. XXVI, figs. 5 and 7). 



A similar type of spicule to that figured on Plato XXVI, tig. 9, c, 

 is also commonly found in perfectly typical specimens of E. fluviatilui, such 

 as that figured un I'l. X.WII, fig 4, Again, if spicules, such as those figured 



