50 The Irish Naturalist. March, 



Planorbis carinatUS, MirlL — The few mdividuals of thi.s sjiccies are not 

 typical. They are ver\- much compressed, and the striae are much 

 more pronounced. It is a form which is. not uncommon in Ireland 

 though, according to our experience, it is abstmt iroin England. 



Planorbis vortex (Linn.). — The representatives o( thiis species agiee 

 with the i'. L'<inpr(-.isus, Mich., of French authors. 



Ancylus fiuviatilis. Midi. — Two forms oi this species are preserit. tho^e 

 from L. Vearty and L. Derg being only half the size of the examples 

 from Lower Lough Erne. The occurrence of these two forms was pointed 

 out over fifty years ago by W. Thomp>son. and we are still nnable to 

 .say whether there are two species or whether the difference arises from 

 environment. 



Physa fontinalis (Ltnn.), — Of thi.s also two forms are represented, a 

 large form. /'. Taslei, Bourg., and a smaller form, P. Coronadoi, Ser\-ain 

 hut as yet no valid reasons have been adduced in sup[x>rt of the view- 

 that the P. fontinalis (I^inn.) of English authors should be considered an 

 aggregate species. 



It is of course possible that it is an aggregate, yet, when one consichr-, 

 the great variation of some species of this genus, one may well hesitate 

 in accepting this view, on the ground of small differences in the shape 

 of the shell. 



Valvata piscinalis (Mall.). —All the examples of V. piscinahs would 

 be named V. alpatris, Blauner, by most Continental authorities, but we 

 are in agreement with Dr. Bollinger in considering this so-called species 

 as only a mutation of V. piscinalis. (Zur GastrofKxicnfauna von 

 Basel und Umgebung. Basel, 1909, p. 165). We would, however, 

 point out that in these islands this form has a decidedly western range. 



Bfthynia tentaculata (Linn.). — Many of the examples are much eroded 

 at the apex anil decollated, this being most pronounced in the shells 

 from L. Vearty and L. Shivnagh. T\\e shells from the smaller lakes 

 are decidedly .smaller in size than those from Lower L. Erne. The 

 largest example from the last-named lake measures 13 '9 by 8-5 mm. 

 and apjiroachc-s the var, producta Menke of Continental authors, whilst 

 from the smaller lakes none exceeds 11 mm. in length. 



Sphaerium comeum (Linn.). — All the examples of this species are small, 

 being much smaller than those found in the south-east of England. At 

 the same time there is but little difference in size between the shells from 

 Lower Lough Erne and those from the smaller lakes. Some of the 

 examples from Lough Vearty and Lough Tullynasiddagh are small but 

 very much inflated, some examples measuring 7 by 6 by •.' •, mm., 

 presenting a very different appearance from typical comeum. Since. 

 however, this species varies greatly in inflation, and the extreme examples 

 can be graded into normal connttnu we have come to the conclusion 

 that it is a local mutation arising from environment, and in this view 

 we have the support of A. VV. Stelfox and K. Welch. M.K.L.A. 



Pisldium. — The members of this genus were, on the whole, pooily 

 represented ; at no spot were many individuals taken, frequently only 

 one or two. The greatest number of species were found in L. Acapple. 

 L. Shivnagh, and L. Derg. 



