353 



PISIDIUM LILLJEBORGI Clessin AND OTHER PISIDIA 

 IN CARNARVONSHIRE. 



By CHARLES OLDHAM. 



(Read before the Society, April loth, 1912). 



I SPENT a few days in September, 191 1, at Capel Curig, searching 

 in the lakes and mountain tarns — with ultimate success — for P. Hllje- 

 borgi, and incidentally I collected several other species of Pisiduan. 

 In the mud of a small reservoir at Llanrychwyn (700 feet) P. snb- 

 tntncatn?)i occurred in great abundance, but in the natural lakes and 

 tarns Mollusca were scarce, and an hour's hard work often resulted 

 in a blank or produced at best three or four specimens. 



The tarns, one and all, have hard, stony beds, almost devoid of 

 vegetation. Here and there little patches of sandy grit may afford 

 an anchorage for the roots of Lobelia dortmanna, Isoetes, or Spar- 

 ganium affine, but such conditions are not congenial for Pisidia, and 

 it was only where peaty mud occurred, capable of supporting Equi- 

 setiim and Potamogeton, that one could hope for any measure of 

 success. The lakes on the northern flank of the ridge which extends 

 from Carnedd Llewelyn to the Conway Valley — Llyn Dulyn, Melyn- 

 llyn, Llyn Cawlyd and the rest, away to Llyn y Pare near Bettws- 

 y-coed — have all been requisitioned as water supplies by the coast 

 towns or by industrial concerns — lead- mines and the like. Their 

 waters, after the long dry summer, were much below their usual 

 level, and two long days' hunting in them yielded nothing. The 

 tarns in Nant Ffrancon and Nant-y-Gwrhyd gave better results. In a 

 small patch of peaty mud in Ffynnon Llugwy (1,786 feet) occurred 

 a beautiful form of P. pukheilum, pale yellow in colour, thin in 

 texture, and with the grooves in the line of growth much less pro- 

 nounced than usual. On the rocky shores of Ffynnon Lloer (2,250 

 feet) a little mud had accumulated in crevices between some of the 

 big boulders, and by sifting this I got a few specimens of P. pusilimn 

 and P. milhnn. A small form oi Ancylus fiuviatilis abounded on the 

 stones in the bed of this tarn ; and I also took a few small dark- 

 coloured Ltvincea pereger. Llyn Ogwen (984 feet) yielded a single 

 P. obtusale and a distorted example of Planorbis contortus. In Llyn 

 Idwal (r,2oo feet) there is a considerable area of peaty mud, and here 

 among Equisetum and Scirpus I got about a dozen specimens of P. 

 lilljeborgi and one P. casertanufu in an hour-and-a-half. The neigh- 

 bouring Llyn Bochlwyd (1,900 feet) yielded only P. casertanutn, as 

 did Llyn Cwm-ffynnon (1,254 feet). In Llynau Mymbyr — the Capel 



