Stkphens — The Fresh-water Sponges of Ireland. 223 



in Lougli Boy, County Cork (1,800 feet), and in tluj oul-ilinving .slruam. Jn 

 addition, spicules belonging to the species were found mixed with specimens 

 of Ileteromeyenia h'l/dcri from Lough Eagher, County Kerry (1,550 feet). 

 If. Ii//dcri, which almost invariably accompanies /S'. /«c;(.s/?'i.s in non-limestone 

 districts, is much more commonly found in tliese mountain tarns ; but it is fo 

 be noted that S. laciistris alone was found in the little tarn at 2,200 feet on 

 Mount Brandon, which is the highest altitude at which a fresh-water sponge 

 has been found in Ireland. 



In many of the low-lying lakes and rivers the growth of S. lucusiris is 

 vigorous, the skeleton spicules are robust and are united into thick fibres by 

 a considerable quantity of spongin, and microscleres are present in the greatest 

 abundance. For example, the species was seen spreading in masses several 

 square feet in extent over a large boulder in Lough Feeagli, County Mayo. 

 The pebbly bed of the River Shannon below Lough Allen was literally 

 carpeted with branched and unbranched specimens. An equal profusion of 

 specimens was seen in similar situations, while in the tree-bordered stretches 

 of some of the rivers in tlie south-eastern part of the country the species may 

 be seen coating the tangled roots of alders for yards along the banks. 



The skeleton -spicules in these large specimens usually vary between 

 0'2-0-3mm. in length, and have a maximum thickness of O'Ofomm., or more 

 rarely 0'015 mm. The free microscleres are as a rule between 0'07-0"12 mm. 

 in length, and have a maximum diameter of O'OOS mm. The gemmule-spicules 

 vary between 0'05-0-13 mm, by 0-006-0-01 mm. (PI. XXVI, fig. 1). 



The gemmules themselves have no granular layer, or, if present, it is 

 poorly developed. Very rarely it is well developed. 



A great contrast to this vigorous growth of S. lacustris is presented by a 

 certain form of the species which is characteristic of the mountain lakes, and 

 also of the low-lying western lakes of the non-limestone areas (PI. XXVI, 

 iig. 2). This form occurs in small, more or less oval, patches on the under 

 surface of stones. These patches are thicker towards the centre and thin out 

 towards the edges. They are pale yellowish in colour, soft to tlie toucti, and 

 slightly hispid owing to the ends of the spicule-fibres projecting beyond the 

 dermal surface. One or more small oscula are situated towards the centre of 

 the sponge. This form of >S. lacustris is easily distinguished at siglit from 

 the lake form of Heteromeycnia Ryderi, witii which it is almost invariably 

 associated, by its colour, its greater hispidity, and niDre particularly by its 

 extreme softness. 



The main skeleton-fibres are very slender, usually between O'Olo-OlU mm. 

 in diameter. These are united at fairly long interv als by transverse fibres, 

 consisting of a single spicule or of a bundle of a few spicules at right angles 



[2U2] 



