Si'ELFOX — List of Land and Freshwater Molhsks of Ireland, 1 11 



we must abide by the decision of the 

 anatomist, though personally I am 

 not satisfied that they are not old 

 forms of Limnaea pereger, which through 

 long isolation in lakes that have steadily 

 becomemore peaty as timeadvanced, have 

 gradually altered and become dwarfed. 

 In different lakes we find that the 

 dwarfing process has not always reached 

 the same stage ; thus in three of the 

 lakes on Achill Island we find three 

 forms of Limnaea. (Figs. 8, 12.) 



I cannot but regret that new species 

 are added to our list from specimens 

 which experiment might prove to be 

 only varieties caused by environment. 

 Experiment has already proved that 

 environment greatly affects the growth 

 of the shell, but we have nothing to 

 tell us the effect on the radula and 

 genitalia of the animal, on which 

 characters most of these modern species 

 are being founded. There are shells in 

 the National Museum, Dublin, which are 

 apparently normal L. pereger. These 

 are stated to be the progeny of L. invo- 

 luta, reared under artificial conditions. 



Limnaea stagnalis (Linne). 

 Plate VII, figs. 33-37. 



and north-west Donegal. In the north- 

 east, though recorded from the divisions 



WD ED LD AM 

 FE TY AR DO 

 WMSL LE MO 



EM RO C¥ LH 

 WG NG LF WH ME 

 SC KG KD DU 

 CL NT QC CW wi 

 NK LK ST KK wx 



SK MC EC WA 

 WC 



of Derry, Antrim, Down, Armagh, and 

 Tyrone, it is really confined to the basins 

 of the Bann and Lagan Elvers. 



It is worth remarking that the areas 

 of Mayo and Donegal from which this 

 species is absent, are those in which 

 Limnaea aurieularia var. acuta is most 

 abundant. L. stagnalis reaches the 

 west coast in the sand-dune lakes of 

 "West Mayo at Louisburgh, but does 

 not live on any of the western islands. 

 The most interesting variation in the 

 present species is that which is to be 

 found in Lough Neagh and several 

 other large lakes, and is similar to the 

 var. laeustris of Studer, being smaller, 

 thicker, and more tumid than the type. 

 (Figs. 36, 37.) 



Relix stagnalis, Brown, Mem. "Werner. 

 Soc, vol. ii, p. 530, 1818. Limneus 

 stagnalis, Thompson, Cat. L. fr F. W. 

 Moll, of Ireland, p. 31, 1840. 



Widely distributed but seldom 

 abundant outside the limestone areas 

 of the central and eastern counties, and 

 absent from such peat-coyered districts 

 as West Cork, Kerry, north-west Mayo, 



Limnaea palustris (Miiller). 



Plate VII, figs. 21-26. 



Helix palustris, Brovni, Mem. Werner. 

 Soc, vol. ii, p. 530, 1818. Limneus 

 palustris, Thompson, Cat. L. & F. 

 W. Moll, of Ireland, p. 31, 1840. 



Recorded from all county divisions. A 



