1919. Stelfox. — Lake-Forms of Limnaea pcreger. 9 



NOTES ON THE LAKE-FORMS OF LIMNAEA 



PEREGER. 



BY A. W. STELFOX, M.R.I. A. 



Students of the Irish mollusca are indebted to Mr. H. C. 

 Huggins for his paper in this Journal for August-September 

 last (vol. xxvii., pp. 1 19-128), in which he has brought together 

 some very striking evidence in favour of the idea that the 

 shells known as Limnaea involuta, Harvey, and L. praetenuis, 

 Bowell,are merely phases of the ordinary L.pereger found in 

 almost all our lakes, both mountain and lowland. In the 

 past many conchologists who have visited Lough Crincaum — 

 the original habitat for L. involuta — have expressed doubts 

 as to whether this shell should be classified as specifically 

 distinct from L. pereger, yet the latter course has been 

 generally followed. Mr. Huggins has been fortunate in dis- 

 covering a series of tarns lying close to each other, at about 

 the same altitude, of similar formation, and yet each shel- 

 tering a somewhat differently characterized Limnaea, where 

 the whole problem could be studied within a few square 

 miles. One of the things which prompted me to visit the 

 Dingle promontory in 19 10 was the possibility of obtaining 

 such evidence as that secured by Mr. Huggins from his 

 study of the Caha Lakes. I was therefore greatly dis- 

 appointed in not being able to find any Limnaeae in the 

 higher tarns situated around Brandon I\Iountain. 

 • The only explanation of their absence seemed to be the 

 fact that most of the outlets from these tarns traversed 

 steep, broken ground, and tumbled over numerous water- 

 falls, thus suggesting that the Limnaeae of the lowlands 

 might have been unable to migrate upwards to the higher 

 tarns. It is interesting, therefore, to note that in several 

 of the more remote and inaccessable of the Caha Lakes 

 Mr. Huggins likewise failed to find any of these shells. If 

 there is any truth in my idea that they find diificulty in 

 ascending these steep outlet streams — in spate one week, 

 after rain has fallen ; almost dry at another time, during 

 drought — then we should find the most aberrant forms in 

 the most inaccessable tarns to which the shells have been 



