Sih.iMiKN.s — The Fresh-water Sponges of Ire.laml. 245 



'I'lic I'oregoing siuni-tyiiical U\\\\\ Iciulw on lo tlicj Bakni riniu, wiLli very 

 sleiulor spicules, wliicli grows in lakes, wlieie llic coniliLions are still more 

 unfavourable to robust grovvtli, and wlii^rc tbe sponge only exists in small 

 numbers, as already described. 



//. Byderi occurs in tlie semi-typical form jusL referred U) in most of the 

 mountain tarns l}ing at or above tlie 1,000 feet contour, and it lias also been 

 taken in one or two lakes at a rather less altitude. The maximum size of 

 the skeleton-spicules is 0'27 mm. in length by 0-OOS mm., or, in a few speci- 

 mens, O'o mm. by O'Ol mm. In three or four lakes, at or about the 1,000 feet 

 contour, specimens of H. Byderi occur which belong to the jjidovcMsis group. 

 But in all these specimens the spicules are more slender than in those 

 specimens found at lower levels, their maximum thickness being O'Ol mm. 



Thus the spicules in specimens in lakes lying at higher levels apparently 

 do .not reach as great a thickness as tliey do in low-lying lakes. The spicules 

 of specimens in mountain streams are, as a rule, also slender. On the other 

 hand, all the specimens belonging to Group HI have been found at low 

 levels. Potts (31) stated that "the spicules of all species [i.e. of fresh-water 

 sponges] increase regularly in size and solidarity as we descend from high 

 altitudes towards the sea-level, where is found the extreme of the series." 

 The author also stated that he had traced the working of this rule more 

 particularly in several variable species, among them H. Byderi. Three 

 years later he again referred to this rule (33, p. 240, foot-note), but in rather 

 less dogmatic language, citing as well some exceptions to it. Hard' and fast 

 rules cannot be laid down where fresh-water sponges are concerned, yet, on 

 the wliole, it appears to be true that specimens of H. Bi/dcri occurring in 

 lakes in Ireland at higlier altitudes do not possess spicules of the maximum 

 thickness for the species. At the same time, it must be remembered that 

 specimens with very slender spicules are often found in low-lying lakes. 



LocALrriEs. 



Kekky. — L. Cooniasaharn, L. L'ununernaniuek and ouL-llowing stream, 

 Caragh L. and Caragh K., L. Yganavaun (coll. Hon. M. Spring liico and 

 Miss L. Stephens), Middle L. and Meeting of the Waters, Killarney ; 

 L. Avoonane and out-ilowing stream, L. Doon (21) and out-llowing stream, 

 L. Duff and out-llowhig stream, L. Gall, stream from L. Nalackeu (1,000 ft.), 

 L. Cruttia (coll. R. Welch), L. Camclaun and out-llowing stream, Coumanare 

 Lakes (1,250 ft.) and out-flowing streams, L. Adoon, Cloonee Loughs and 

 Cloonee R., L. Inchiipiin and out-ilowing stream, L. Cummeenadillurc and 

 out-flowing stream, L. Eagher, 1,550 ft. (38;. 



