10 The Irish Naturalist. January, 



able to spread. The reason for this being that the arrival 

 of new blood would be greatly restricted by the difficulties of 

 the passage from the reservoir of the species in the adjoining 

 lowlands. My own work in the West of Ireland has led me 

 to believe that there is something in this suggestion, and 

 Mr. Muggins's evidence rather tends to strengthen this 

 belief. 



To return to the larger question of whether L. involuta, 

 L. praetenuis and the lake forms of L. pereger are variations 

 of one polymorphic species, I may say that I arrived some 

 years ago at the same conclusion as Mr. Huggins has, by a 

 study of the different forms of Limnaeae I had collected in 

 the tarns of Kerry, Ma^^o and Donegal. In working up the 

 Irish list in 1910, nevertheless, I listed involuta and prae- 

 tenuis as distinct species out of deference to the anatomical 

 evidence, which seemed to carry great weight in certain 

 sections of the conchological brotherhood, though compared 

 with m}^ own experiences in the field it meant practically 

 nothing to myself. Perhaps it is due to having held these 

 views so long that they appear to be substantiated so satis- 

 factorily by Mr. Muggins's evidence. It is also pleasant to 

 feel that yet another man who has studied the question at 

 first hand has come to similar conclusions ; and especially 

 so as since the publication of my views in 19 10 and again 

 in 191 1, the contrary theory has been upheld by Messrs. 

 Kennard and Woodward in their work on the post-Pliocene 

 mollusca of Ireland.-^ Not only have the authors of this 

 valuable paper considered L. involuta and L. praetenuis to be 

 distinct from L. pereger, but they suggested that they should 

 be placed in a separate sub-genus — C3^clolimnaea of Dall — ■ 

 and they have transferred them to the opposite extremity 

 of the Limnaeidae from the L. pereger group ; at the same 

 time professing to believe that it has been proved that the 

 affinities of L. involuta and L. praetenuis lie with L. glabra 

 rather than with L. pereger. 



Old delusions are difficult to eradicate, and erroneous 

 statements once in print get copied long after they have 

 been contradicted. Thus in the recent (1911) monograph 

 of the Limnaeidae of North America Mr. F. C. Baker, in 



^ Proc, Qeol. Assoc, vol. xxviii., p. 173, 1917, 



